[chiphead]

Either 400 or 400 block with stroker kit.

The 389 and 350 have the same stroke as the 400 (3.75") but much smaller pistons. The 389 is the predecessor of the 400. The pistons on the 389 are .060" smaller and the heads are more restrictive than the 400 heads. But the 389 is no slouch, it was just replaced by the 400 in '67.

The 350 is a smaller engine that came out in '69 to replace the 326. It has smaller pistons than the 389, and it suffers from valve shrouding because the bore is so small. It will still run, and capable of 325 HP when hopped up. You can't bore it out to a 389 or 400.

Most people build 400s, because the cost is the same as a 350 and you can get another 100 HP out of them at the same level of tune. But the current trend is to stroke the 400 block to 460-488 cubic inches using stroker crank kits. 450-550 HP is the norm for those engines on pump gas and with good street manners!