Its pretty widely held amongst hotrodders that the 7.5 rear is not a great choice for any performance vehicle. I've personally seen several of them grenade behind motors that weren't that wild (sub 450 horse motors). Sure, it depends on hook-up etc. I don't know what you intend to do with this car, but for my money a rear end is kinda worthless if its killing your 60' times because you can't afford to put the coals to it until you're already rolling.
I'd also say that the "wait and see" philosophy isn't a really good choice. You can break a rear end and be lucky, the best that happens is you have a little unexpected work and some expense. Of course, you could also grenade the thing and lose control of your vehicle, or get some damage to your car.
A more stout rear isn't a huge investment. In all honesty it would probably be the first thing I'd get for any performance vehicle. No sense in doing work twice or risking safety-