Let's see, out of time, burned valve, stuck valve, valves adjusted too tight, stretched timing chain, flat cam, crossed plug wires. What is happening is this, the plug is firing the mixture in the cylinder, a valve is not sealing the explosion. Or, the spark plug is firing at the wrong time, thus igniting the "charge" in the exhaust, or intake manifold. In other words, the valve, and ignition timing, (spark) are out of sync.
Unburned fuel in the pipes. Your running a little rich, or, maybe the float level is a little high in the carb.
That would be a small block.
A cylinder is misfiring.
No. You would need to have the main journals turned down .200". Then it would fit.
no modifications necessary
Many. 348 would be a small block, whereas the 454 is a big block.
Everything
That would be a big block. If you are referring to the diesel engine, it is based on the Oldsmobile rocket block, and shares nothing with the engines usually referred to as big block or small block.
The 350 is the small block, and in 1986 it would be GM corporate blue.
no
It would never hold together.....
One of the valve covers.