1. 1947: 114" wb vs 1935-40 (41PU&SD) 112".
2. 1947: 3" wider track width vs 1935-40.
3. Parallel leaf springs on 1947 vs transverse 1935-40.
4. "ladder" frame on 1947 vs shaped frame with x member on 1935-40.
Using the 1939 frame, mounting the pickup body, and converting to 1940-41 front sheetmetal (or fiberglass... hint, hint) and grill is very reasonable (the 47 bed will need to be narrowed 3"). Trying to use the 47 sheetmetal on a 39 frame will be a nightmare, as would trying to use the 40-41 sheetmetal on a 1947 frame.