The bigger and heavier the engine? The harder a 72 Mustang will handle. You'll need to beef up suspension. Get no more power than YOU can handle. That car will toss you into a telephone pole. Or, sailing off the road in a corner faster than you can blink. Untrained. So, don't just toss a 500hp motor and think both you and it are now All That. You won't be. Even though you make the car a beast. Get experienced with it on a track before you go street warrior with it? I mean that nicely too. Seen too many fine cars with with green drivers get into a mess.
Anyway, The finest stock Mustang setups involved the 427, 428 and 429's You may increase horsepower at will with these. Modern setups seem to like the LS-1 series. A great balance is a strengthened 302/351 series with EFI and high compression.
Select your flavor engine/trans setup and have fun!
The 454 is what I use as an anchor weight. The 351W in the small block builds are the way to go. They are lighter than big blocks, and are big block build capable in terms of hp and torque. And also a little lighter than a Cleveland which is like a needle in the hay stack to find. Unless you purchase an after market block. The "W" can also take the "C" heads called a "Clevor Engine". But the Canifield, Brodix Neal and Blue Thunder heads are just as breathable. How about a 486 C.I.D Windsor small block? 900hp capable on a good build.