Is it wise to push a 7 1/4?

Yes it is very wise to push a 7.25 rear...right into a scrap pile. Unless want a tow bill, wait till you finish your 8.75 rear. But if you have to do it, do a burnout in front of your house. This way when it blows up, you're a lot closer to home and won't have to tow it but you'll still be waiting for the 8.75 to be finish. That said you might find yourself finishing the 8.75 a lot sooner than you thought.