Engine decking issue(help)

MoparMark91 said

This is a 340 block with a 3.58 crank fron scat, dont 318 and 340 share same main size?

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Yes 273, 318, 340 and I think the V10 all use the same rod bearings.
The 273, 318 and 340 use the same mains up untill the1974 middle bearing change.