thought I would post some info if anyone has an interest. I am about 1 year into my purchase of a Comet 108 4Pro, the 4 pro is different than a 108 in that is uses 4 weights and rollers.
I have this setup in my pilot with a 670 rotax, the clutch comes without the spring or weights I purchased 4 weights P/N 213370 A1, at 44.7 Grams each along with the purple spring P/N 207758A
The clutch come setup for a snowmobile belt, it has the holes drilled and tapped for the Skidoo starter ring.
It is possible to disassemble the clutch and pull a couple of spacers to make this fit a Pilot belt, if you live close to a shop that has the tools and can do it cheaply you may want to go that route, the tools can be purchased but that will cost you around $150, I opted to use a wide belt, it does not fit into the driven clutch very well but it lasted all season without mods.
The Belt I found that worked for me in an carlisle ultimax 131-4126U4, I figure it does not spend much time at the top of the shives.
the clutch setup works pretty well, sorry I don't recall the exact RPM that it kicks in and what it holds at, I believe it was around 4700 to hit and it was reving out to about 7300 or 7400, I wanted it to rev a little higher to start and run out higher as well.
Comet has a Spring shim kit P/N 203849A, it basically just pre-loads the spring a bit, comes with 3 shims and each shim is said to be roughly 200 RPM higher, that is engagement and what it runs out at, I put 2 in and now it runs out at about 7800 which is where I wanted it, I believe that is peak power for the Engine, it would be nice to dyno some time as I know that with the seadoo carbs, not stock airbox and modified pipe it has to be something different.
That's it, I'll dry to get some numbers and video of the tach running on the flat later this month.

A couple of down sides of the 4 Pro, it cost a little more that a standard 108, it uses 4 weights so there is an extra cost as well and it weighs a little more.
the up side, it should be stronger sharing the load on 4 slider rails and from my understanding you can do more fine tuning by using different weights, 2 of the same opposite each other, the Comet has quite a few weights to try, I wish others were using it so I could use their info

Thanks for the information! I got the 670 in my oddy. I am going to be using the skidoo clutch for now but this may be a good upgrade in the future.

What are the advantages over a TRA clutch? I've had decent luck with TRAs.

Cool info
A is missing from list. Hope it is the same as pictured.

I suppose if you are getting a new TRA it should be good but I had a TRA explode on me and another cracked, after checking my crank had some run out, did the run out cause the clutch to fail or did the clutch failure cause the crank issue? I have no idea.
the 4 pro has the 4 legs and the TRA has 3 so the load is reduced, at least that was my thinking, I did not want to get another Ebay TRA as it could be that it is not a matched set and the balance might be off.
before the TRA let go, it seemed to work very good, it does have good tunability and in the Ski-doo Race manual there is a lot of good info regarding tuning the clutches.

FYI, here is the Comet web site, they are a part of Certified Parts https://www.cometclutches.com/#

here is what came with the spacers.

Page 2 has good info for setup

I have a question on the Engine placement.
Is the crank to trans input shaft centers the same as a stock pilot?
Wondering if I do a full clutch swap to a wider belt set up if I need to consider that center to center number for the wider belt.

Neither of my Rotax swaps use a stock belt.

The big issue here is the stock Pilot driven. I have a problem with running the belt too far past the cords on the driven. It'll rip the inner teeth off the belt eventually. I guess some kind of spacer can be made to widen the shivs about 1/8"

Also I want to mention the importance of the wider belt with Rotax. I've damaged 2 belts recently and I believe the wider belt and proper clutch setup is key to longevity.

This is setup using a mount that I built that should be the same as the Farr mount, I can get a measurement but it will be a bit of a ballpark figure since the centers are not on the same plane.

As the belt does not sit into the driven clutch I believe it is longer than stock can cross reference the belt number and get the length.

When I had the TRA clutch I was able to modify the drive clutch to run the stock width, I did go through belts but I figured they were a consumable and usually still under warranty

so far on the wide belt running on the stock driven, I haven't had an issue and still looks pretty good after a hard sand season, knock on wood.
if you were to space out the driven to get the belt to ride lower you would need a shorted belt, short wide belts are hard to find, not sure if you would be able to locate. I figure the belt doesn't spend much time at the top of the driven anyway, I think I'll put a gopro looking at it to confirm.

Don't worry about it. Next time you pull it apart get the measurement. Thanks

A little update on this, it seems the clutch was making a lot of noise, at least I'm hoping it's the clutch, I pulled it off, it has a 5/8 fine thread in the snout, I used the hydraulic method, got the pilot tilted enough to fill the clutch end and crank full of water, Teflon tape on a 5/8 fine bolt, a little grease on the threads to help get it starter and popped it right off.
now you need special tools to pull the clutch apart, I am much too cheap to spend $150 on some special tools so I spent the better part of Saturday morning making something, it worked I did not waste my time.
The bushing on the movable shiev seam warn out and there is way too much slop between the towers and the buttons, so I have a new bushing ordered from Ebay for about $23 and new buttons ordered from Comet for about $45, this is after 1 season of operation, no telling when I should have replaced them 1/2 season? kind of an expensive wear item to maintain. once done I'll report back.