318 4" bore 3.58" stroke(360)

Bill Crowell said
FWIW, don't forget that you'll have only the 2.5"-diameter main journals in that 318 block, rather than the 2.81" journals that the 360 had.

Maybe the 2.5" crank journals will be fine, though. When the Chrysler engineers designed the 360, they intended it to be a real fire-breather with free-flowing heads that would kick the Chevy 350's butt, and that's why they increased the main bearing diameter. However, then the smog laws kicked in, so the 360 engine could never be developed to generate the amount of power that the Mopar engineers had originally intended.

...or they could've increased the bearing diameter for longevity especially in truck applications where heavy loads are ever present...but even that's a stretch. Only Dodge knows how many full size pickups ran for 200K miles any beyond with the modest little 318 and never exhibited any issues even with the smaller journal size.

Beyond that, the standard journal size will not affect the longevity unless he starts spinning it too high for the oiling system to keep up, or higher than the crank can live. In short, the block itself is puh-lenty strong.