actually i would make a 390 out of the 318,

KB makes forged pistons for this combo...flat top and dish..

you couse use stock rods or get a set of scat i-beams...

pick up a 4 inch cast crank for 250 bucks...about what it will cost to cut the 360 crank to 318 journal size.

just something to look at...

also Mahle makes 318 3.58 stroke pistons...seen them on ebay a couple of days ago...not cheap...around 550 bucks..

there is probably a cheaper route to go on that combo also.