Looking for help w/ 7 1/4 rear end

Hello,
I the process of rebuliding a 71/4 rear end for my 1970 dart. Went through the carrier setup. Machined new shims. Wondering if anyone knows where to look for a Spreader Tool C- 3721. I made one out of 1/8th wall square tubing. I could only get .007 spread before it bent the tubing. Or if there are any tricks?
Thanks,
Jason