I would say that you will need '46 inner fenders and core support, actually a complete front clip off of a '46 would be a big help..
The '46-48 axles, front and rear are not a problem under a '41.. True the tract is 2" wider, however, the only solid attachment point is at the front/rear spring.. A '42-48 springs will be needed along with the tie rods, etc.
Of course if you are going to street rod the car, the use of an independent front end, (TCI, FatMan, etc) would be the best answer..
I know that the basic body shell, '41-48 are all the same.. In 1951 I was working in a body repair shop in Eastern Idaho.. We had a '42 coupe that had been rolled. It was not going to be a big deal to fix the car, that is until we discovered that the car was an Eastern US car, the bottom of the car was badly rusted out.
We had a '41 coupe that had been hit head on, it was a total so it was going to the wrecking yard. Did some checking, the basic body shells were the same. We cut the cars at the "A" pillars and across the floor at the factory seam. The rear section of the '41 was then grafted to the '42 cowl.. We took the transformation to the next level, putting a '46 grille into the..
That's the way things were done back in the day of "old school repair"...