[blykins]

IMO, the short stroke crank and rods would be your best bet for turning high revs. But the difference would probably only be noticeable in REALLY high revs.

How high are you looking to spin it?

The 390 with stock rods wouldn't require any special pistons....neither would a 3.98" stroke crank with stock 6.490" rods.

They use 6.700" rods with 4.125" and 4.25" stroke cranks....so pistons are readily available for those combos.

To use a 3.98" stroke crank with 6.700" rods would require a compression height of 1.480" on a stock deck block and I think that would be a custom piston.

There are lots of theories on rod length/stroke ratios...so you'll get a bunch of difference answers on what the optimum length rod would be.