I recently purchased a 1985 Silverado and the previous owner said he thinks the motor has a bent valve. I am new to this and want to try and troubleshoot this issue prior to purchasing a new engine all together.
The engine turned over and all the valves on the drivers side were moving but it never fired. He said that it does start but that it backfires a lot in this condition. The motor is a 350 and it does have aftermarket intake, cam, heads etc on it.

Can anyone provide any guidance so I can get this truck back on the road please?

Thanks