Time to change out rearends.

Another question. Before I go thru the trouble of torching the old U bolts off the 7 1/4. I was wondering if I could use the ubolt mounting plate on the springs.
I was thinking since I am a machinist, I could slot the old holes to fit the new ubolt for the 8 3/4, but I'm not sure slotting the holes is a great idea. Otherwise I could weld in the old holes and redrill. Anything else to worry about?