Big Fat Rear End!!!

Ok, I have this 1951, Chevy Pick up. I was told that the rear end came from a 1957 Chevy. But supposedly it is from a 1958 to 1964 Chevy Car. The bearings and seals I bought for it were the wrong ones. that is how I found out it was actually for a 58-64. So,,,to make a long story short. to replace the bearings and seals in it will cost me like over $225. I just figured I could replace the whole rear end and maybe get Posi- to go with it. What should I do? What would be a good inexpensive replacement? What size should it be? Can I use Dana? and Where can I get one?

Thank you,
Matty