Changing the cyl bore does not affect the ignition timing of the engine.
That means the timing chain and gears are worn out / to loose.
I would set it by ear, and performance.
cam timing will not change ignition timing i would try 8 or 10 degees advance at idle with the vacuum advance disconnected.
A 383 Chevy is a 350 block with a 400 crank bored .030 over. If it's not bored oversize it's a 377 (Not the only way to make a 377). If it's .060 over, it's a 388. Most builders agree that you cannot safely bore a 350 block .090 over, but if you did the resulting engine would be about 394.
It would only be possible to answer this question if you provided enough information, and in one system of measurement. What is the stroke of the crankshaft? Also, will the block be bored oversize by .040"? It seems unlikely that the intent is to bore a block .40" as there would be no wall thickness left, and .40 mm is .015" which would require custom made pistons as it is not an off the shelf size.
A 402 is really a 396, bored .030 over, already. .120, is about all there is before you hit water, so, another .090. You can sleeve the block, and go further, however, at that point you would be better to with an aftermarket block.
timing is off!!!! If it has points, check that the dwell is 30 degrees. Be sure the ignition wires on are correctly. Verify the carb is not rich.
on a vehicle that old and i am assuming that it is carburated would be mounted to the engine block off to the side close to the timing cover!
327/275 and 300hp, 8 degrees btdc.
It would be more normal to say "bored with something"
Yes. That would be a 350 bored .030" oversize.
That would be to the left of the timing pointer Or left of ZERO TDC