Welcome Scott,
I visited the WR shops in Birmingham a few years ago and they had that same model on display. Caliber was 450.No 1 and I would agree with Huvius and recommend that caliber on your rebuild. I would also discourage the 450/400 idea, someone might slip up and drop a NE round in there thinking if it fits it's OK. I'm in Savannah and also load the 450 No.2 if you need a bit of assistance. Looks like a good, do-able project.
Best.