I would build the higher power engine with the Eagle crank, and put the checked factory crank in the spare/back-up motor. If the factory crank is already balanced for the 452, use that block for the back-up and put the primary/higher power setup in the 448 block. No sense in rebalancing for 4 CID.

IMO, the factory crank is good to use. But it will need to be magnafluxed on a regular basis to be safe. So depending on use, once a year or so (maybe 2 years for you since you don't run it very much).