All small blocks share same crank ?

The 360 had larger main bearings and as stated a larger rear oil seal area.
ALL 360 factory cranks are cast.

ALL 273, 318 and 340s use the same size main and rod bearing.

All mopar small blocks use the same size rod bearings, 273, 318, 340 and the 360.

The factory used both cast and forged cranks in the 272, 318 and 340s. Each had its own balance requirements.
Yes you can use a 273 crank in a 318 or 340 but you may need to rebalance it.
Some of the 273 &318s have a differant size on the back of the crank where the converter engages it.