Are old style 302 and 351 blocks the same? If one wanted to upgrade a 302w to a 351w.
If i remember correctly,late model 351 heads flow the same as the 302 so if you are upgrading the heads the ones to get are the early style.... But the difference are the bolt size on a 351 windsors are 1/2" and they are 7/16 on 289/302...late model heads have 1.78 intake & 1.46 exhuast valves and early ones have 1.84 & 1.54 & also slightly larger intake and exhaust runners.
Ford began using the same basic head casting for both the 302 and 351W in 1977.
These later 351s, originally identified as 351Ks, have the rectangular 302 intake water passages and 6 intake manifold bolt holes. Original 351W heads have L-shaped water passages and 8 intake manifold bolt holes.
Also, the late model 302/351 heads have a larger water passage at the rear,
which means the intake gaskets are different between early and late models.
If you swap "real" '69-'76 351W heads onto a 302 you need to use the
351W style intake manifold gaskets, as the 302 gaskets will leak water
at the unique 351W intake manifold water port
You do sometimes need to drill out the steam pocket relief holes (there the real small holes you see on the head gasket) in either the block or head when swapping between 302 and 351 windsor parts. You use the head gasket as a guide. You just make sure each one in the head has a matching hole in the block.
All 351 block 69 though present has been cast to accept the 3" main crankshaft bearings that all 351's have, you can't stick a 351 crank in a 302 block it wont fit, the bare blocks look similar side by side and anyone who doesnt know couldn't hardly tell them apart, but if you flip them over and look at the mains you'll see the difference, they beefed up the 351 mains to handle the added stress of the longer stroke, hence what Bubba said "oil pans won't swap" thats because of the larger mains, yo Bubba you didn't mention timing chain covers I'm thinking you can't swap them either?