Don't think you'll need to space out the flywheel, NV-4500 conversions have been done before on these engines. Go to Jolly's 6066GMCguy.org site, there is an NV-4500 conversion in there. Some custom pistons with 3 rings, Chrysler 426 Hemi type rods with a turned down and stroked crankshaft will result in a 500 plus cubic inch screaming V6