So what happens if you keep the old /6 rear end after 360 swap?

I must've had better luck than most.. I converted from slant six to a 360 2 years ago.. wasnt enough money in the project for a new rear, so the 7 1/4 stayed in.. Its a sure grip 7 1/4 and I drove the car for 2 seasons this way.. and I was in no way gentle. Even drove it on a 3 hour, one way trip to the Mopar Nats last August. Burnouts in the alley, you name it (with the exception of something rediculous like a neutral drop) and it just kept taking the beating.. Decided 2 seasons was enough pushing my luck though and bought a complete 8 3/4 at the Nats... 7 1/4 was still good when I pulled it out.. must be a fluke.. All I have ever heard is that they cant take any punishment LOL .. this thread confirms it.. lol

yes you were lucky , I blew the 7 1/4 in my dad's 72 duster when I was 17 and it had the stock 318 with a 2 bbl and a shift kit in the stock 904 still .

The first 489 3.23 chuck didn't last long when the car was switched to a 340 and a 4 speed