Is a 7.25 rear strong enough?

My thoughts. A 71/4 is stronger then most give it credit for. I ran 3.91 SG 7 1/4 rears for years in my drag and street cars. My 66 Cuda weighed 3250lbs had slicks and a 170 slant six with a nitrous fogger system. It ran low 13's in the 1/4, with that rear. That said, I wouldn't use one today. Parts are hard to find, and expensive when found. The 7 1/4 and "A" body 8 3/4 both also have a problem with finding 10 X 1 3/4 brake parts, and both have the small bolt pattern which limits wheel choice.
I would suggest going with the 5x4 1/2 disc brake kit, and a rear with 5 x 4 1/2 other then the 7 1/4. There are several options for a rear.