65 lb compression doesn't sound very much but could be fairly normal on a fairly highly tuned 2-stroke at kickstart speed, especially if the piston, rings and bore are dry.

Exhaust tuning causes a 2-stroke engine to grow in capacity when it is "on the pipe" resulting in a sudden increase in compression ratio and pressure and so if this is not to cause devastating detonation the designer must make allowances and probably utilise electronic automatice timing retard. Starting with a lower compression ratio is another method.
Having said that I would have expected at least 100 psi pressure and probably a little more...

Assuming you checked the new cylinder thoroughly before fitting and ensured all the ports including the transfer ports are open and correctly line up with any ports or recesses in the crankcase and ditto with the base gasket...
Assuming you checked the piston size matched the new cylinder and the piston rings were correctly gapped prior to fitting...

These things should not be taken for granted and should be checked to ensure they are correct. Assuming you did these things and assembled everything correctly (especially getting the piston the right way around) with a smear of clean oil a good induction should be assured and the compression should be almost as good as it is ever going to be.

I suggest you ensure there is a good spark and fuel is reaching the cylinder. If it isn't I suggest you revisit the new parts you fitted and the way you fitted them before investigating anything else.
Good luck!