Advice Needed - Can't Start Rebuilt 273

I had a similar case with low compression and the engine not wanting to start. I checked the valve timing and it was out, I had installed the timing chain using the wrong indexes and it was a few teeth off. You can check the valve timing without removing the timing cover. If you have a factory service manual, follow the directions for checking the valve timing. Even if it`s not the problem it`ll rule out that variable.