I second this advice
another option is to just replace the bad 7-1/4 rear with a good used one,
often times people give them away for free, and you will not need to replace or shorten the driveshaft, or replace your shock plates,
the stock 7-1/4 rear is fine for a daily driver, even with a stock 273 or 318, there are plenty of 40+ year old cars driving around with a 7-1/4", mine included, they are fine unless you are racing or really beat on your car,
