I would keep the 350 NV4500 if it were me. Manuals are more fun in a driver, occasional wheeler. You have a race truck with a serious LS drivetrain, there’s something about an old school SBC that feels good at lower RPM’s in a more mild vehicle. Plus it’s already in there!
The truck is still at my Son’s house in Louisiana, he’s moving back to Virginia this summer, so it won’t be in my hands until then. I’ll let you know the progress, I may go get it sooner if it works out.