You will find that it is almost impossible to replace the rear wheel house in a body with no rust. On a 75 year old car there will be rust where the wheel house is welded to the body floor etc. making it impossible to reattach the souronding patrs. Would be like doing a heart transplant on a 100 year old person.
The was a foam rubber strip between the wheel house and the quarter panel. Here in the rust belt the water soaked foam ruber would cause rust to come through the quarter panel skin.. Was a poor idea in the body constuction.
If it were my car I would patch the bad areas and cover with body seam sealer and or rubberized under coating rather than opening an (expensive) can of worms.
| 
