Sorry Steveon91, I missed your heading "1998 Vortec 355". It would be a one piece rear main seal engine needing an externally balanced crank. (use your same flywheel) Just specify one piece rear main seal and external balance is implied I believe.
You would be better off talking to the Scat salesman as far as the type of bearings, and if balancing is required, that is if you decide to buy a Scat crank. I'm sure they would be happy to help and give you the best info. Might even get a better deal than if you ordered from summit?