Welcome to the site! first off I have YET to do my first sled
Engine swap but do have some info I can give. Quick answer is I would keep it under 125HP. EFI engines are much easier to run...no jetting!
350 trannies are a very good strong tranny with a few weak points you need to know about. They put the same gears n shafts in the "RPM" race trannies(heavy duty cases)....which if you can afford one would be perfect and then you can run nice heavy duty CV axles.
First, the drive line has no slip point. Pilots have a clutch pack that slips under a heavy load. Jumping a 350 under full throttle/wheel spinning hard when you come back down causes lots of flex/torque on everything. The cast aluminum tranny cases can crack under the strain(done it twice).
Next they have needle bearing failures on the AB gear, they tend to fail before anything else, partially because of the stresses of jumping and partially because of the lack of oil being slung on it. Most of us "old timer" 350 guys overfill the oil in our trannies to ensure proper oiling of the bearing. I have also been told(or heard) that idling in neutral spins something in the tranny but doesn't allow proper oiling of bearings too. Not sure about that last one.
Stick with a sled Engine, too much pain in the ass with trying to convert a streetbike Engine with a jack shaft.
Axles are also very strong, weakest point is ofcourse the u joints. The u joint also keeps lateral support...other words if it breaks, the whole hub,tire, trailing arm swings outward and usually bend the shock. Add a limiting strap to save the shock!
Hope that helps some,
Gary