No one can answer this, unfortunately. It depends where your engine is mounted in relation to the frame and body. Since it's a custom installation, it may or may not affect your floor. If you're replacing the complete floor it's your preference, I would probably build my own from scratch. In fact, on my truck I had the stock floorpans but ended up covering over them with 18ga sheetmetal because there were so many holes in the original floor on the 46 that it was just easier to do a second layer over the whole thing.

1946 GMC Pickup - S-10 Frame, 455 Buick, TH400, original patina.

My 46 GMC on Photobucket