rear ends to choose from?

Hello, I was searching through some threads trying to find some of you guys who have shortened your rears. I have a 68 Cuda and putting in a 4 link. I have installed the front relocation perches for the four link and did the mini tub added about 4 inches of metal to the inner fenders. But no one has shared or I cannot find anyone talking about lengths. I am just wondering what some of you have done. How short have you gone. I keep getting told I need to buy the rims then set them in and measure my width. Then it's how to figure the back spacing with no rear-end for the rims. Kind of a circle and I have got it down to maybe 49 to 52 inches depending on which rim I use. Anyone else have what they could share would be great.
Happy New Year!