my cold compression is only at 130. now I am concerned. leak down test passed with no leakage. 6 lb's for six minutes.
just touch the starter and it fire's up and idles fine. went through two heat cycles and a run down the block just cruising after warming it up.
using cometic base and head gasket.
should I have higher compression or has the rings just not seated? if it didn't run so good I would be really concerned. should I be concerned??
thoughts?? suggestions?

Just for your own piece of mind test that gauge.
Check it against the pressure gauge on your compressor. I have run across this issue myself. My Chinese gauge was out (low) by ten pounds. My USA gauge was the same as my compressor pressure.
At the end of the day this thing will run for years.

No-one mentioned this but, your old piston was telling a very LEAN story. Research piston wash (You had very little) and also the underneath part of the piston crown just above the wrist pin is BLACK. It should not be that black. Black in the area of the piston bottom indicates over-heat and some pre-ignition. Get enough heat, and its BOOM - BELOW the combustion chamber. Here-in was why you were back-firing originally. - Lean condition caused by leaking crank seal and low fuel flow all contributed to this effect, and a hot piston bottom caused some explosions within the crank case.

As for your new Engine concerns of compression being low, could be several things. What clearance and ring end-gap did you 'hone' your cylinder for? Clearance figures should be minimal on a new Engine. Who honed the cylinder, and with what kind of hone tool, plus clearance of these parts makes a big difference. All around how tight the clearances are, how perfectly round the hone job was, etc. Break-in should not raise your compression more than 5% (So, 7 psi) IF at all.

Dynamic CR (Compression ratio) is taken from the top of the exhaust port to the head, measured in mm, and then volume of the combustion chamber which is volume of the cylinder head minus volume of the piston crown (Volume of a cone) PLUS the volume of the piston blew the top of the cylinder and squish... complicated..... There are online calculators for getting your CR right. It doesn't look like if from the picture, but if anyone ever ported or shaved the TOP of the exhaust port then you can expect lower compression but potentially better top-end when compression is raised back up with modified combustion chamber volume (CR). Also if you used a THICKER base gasket then you've also raised your exhaust port and changed your combustion chamber volume.

Head gasket thickness, base gasket thickness, and squish band also take, make, or break your compression figures. Your squish band should be no tighter than 55 thousandth. I've read some FL350 run loose at like 90 thousandths (LOL). The larger you go, the less CR and PSI you'll have.