Don't see too many 91 stock 5.0's these days...but there's nothing wrong with adding some mods to make it kick some *** on the street. There's a lot you can do with those cars from completely overhauling the engine to slapping on an intercooled supercharger. I'd post a couple questions in the 79-95 5.0 section, probably get the best responses there regarding your modification questions.
12 Black GT500 SVT PP l VMP TVS l JLT123 l O/R X l 28x11.50Rx15 M/T Street R's l BMR Suspension l Recaros
03 Sonic Blue 3.8 / 17 Magnetic Fusion Sport 2.7 EB