Which 318 should I build ?

toolmanmike said

Both are very similar. The IH block casting should be a good one. (cast in a International Harvester foundry)

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That’s the top block correct....

318willrun said

Build the short block that is the best shape internally.

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BINGO. Sonic check the blocks cylinders and build the one with the thickest walls and hopefully the least rust on the insides.