even compression is as low as 50, it still should start, right?
Not if the timing chain has jumped a tooth or two
I had that happen on a early (1959) poly 318 truck motor, I started it up in the winter, went to back up and it tried to stall and backfired through the carb. It restarted but didn't have any power after that due to the timing chain being worn out and it had jump a tooth retarding the cam timing
The fix was to replace the timing chain and gears with new ones, which it sounds like you need to do also
Get some good help or take it to a good shop to have it tested and fixed properly
