318 rotating mass

The poly 318 uses the lighter '782 rod, which is bushed, so it's easy to remove pistons.
On the pre-'68 engines, the converter hub is smaller and most A/M convertors won't fit, but the crank can be machined for the larger hub.

If you are planning on running a manual trans, the hub size doesn't matter, though.

If you want it as light as possible with stock components, use a cast 318 crank, the weight difference is negligible, but there is a difference, and a Mopar cast crank is more than capable of taking HP and RPMs.

Use the poly pistons with a set of 'J' or '587 heads and your compression will be @ 9.5:1, just be sure to add a notch on the pistons for the exhaust valves.

Don't worry about 2.02 valves, they are unnecessary on a 318, 1.88s will be plenty.

Mark.