The 41 axle uses a "spring behind" set up, the stock Model A uses a "Spring on top" set up. If you are going to use the original spring and cross memeber location you must put new spring perch mounts on top of the rear and you wont use the mounts that were used on the Spring behind set up or you can move the crossmember rearward and use the mounts that are on the 41 rear . Use the search function it has been covered many times in the past
if you have the stock rear end and the 40's rear end you can cut off the top part of the spring perch on the model a rear pretty much ya gonna cut off the end of the axle and than cut that in half so the top 2 holes line up with the holes on the top of the 40's rear and than notch and weld it to save a ccouple bucks ...theres a post on here by chris who is rebuilding his roadster and he did it 1st it looks good also and works great ..find the post and youll see what i mean
Discussed in the Vern Tardell/Mike Bishop book (the Bible). You will also have to shorten your drive shaft and torque tube and use the shorter 46-48 radius rods. From a strength standpoint all banjos from 35 to 48 are the same. 46-48 axles are a couple of inches wider than the earlier models. Something to consider if you are going to run fenders.
Robert, If you are going to this much work consider reversing the housings to place the good side of the bearing surface on the bottom. Whether or not using this rear end makes sense depends greatly on the rest of the project. What are you building? Charlie Stephens