1951 3600 Blazer tank and axle centering?

[bretcopsey]

I am working on adapting a late model Blazer tank to my 3/4 ton '51 and so far had to remove the rear most crossmember that was mounted betweeen the rear leaf spring mounts. I placed this crossmember at the very end of the framerails and now have sufficient space for the new tank. However, there is not much clearance for the differential in the stock location, and I was planning to move it back to center the wheels tot he fender opening.

Has anyone else run into this? If so, how did you corect it? I would like to work with the parts I have to keep the costs down.