I need Help! from the big block Chevy forum gods... PLEASE!!!!

[chevybuilder]

You have tried everything I would have first sounds like. The backfire in the intake seems to me it could be only a few things. Timing error, which might mean the timing chain slipped which would be seen in a compression test in all cylinders, or a burnt valve which would be seen in one cylinder. Timing error would cause it not to run.

[stuff2c]

a friend told me that several years has a plastic timing gear?

I did check the timing and it has a 5deg counting the little marks advance and steady with no jumping around using plug #1 and just using the starter to turn the engine over

[chevybuilder]

I keep thinking while typing. I'm somewhat of a rookie also.