I agree with smokedawg, changing to a 351 would require to begin with a new hood so i won't get into the specifics of that swap. Basically if you have a good induction/exhaust system matched for a higher rpm band and gears and add a supercharger to that you'll EASILY get at least into the 12's. I've heard that a holley systemax kit will get most vehicles anywhere between the mid-high 12's depending on the driving, but then again you have a convertible which is pretty heavy. If money is no object, then my limited opinion is a holley systemax II kit (because it's all flow/powerband matched as a kit), a 9 psi supercharger like a Vortech S-trim, Paxton NOVI2000, etc. at least 1 5/8" primary headers with 2 1/2" dual exhaust, maybe even 1 3/4" with 3" dual exhaust becuase i believe you'd be pushing close to 450 horsepower or even more.
You could also get a stroker short block setup to go with the systemax II (or whatever you choose) like a 331 or 347 to increase torque output for your heavy vehicle and having a supercharger would also greatly enhance your off the line launch.
To go with all the extra power i believe that you'd need things like 30# injectors with a calibrated MAF sensor, maybe even a larger fuel rail, 255lph fuel pump, i don't know but maybe you may need to swap to larger fuel lines in general as well. A custom burnt chip dyno tuned chip would also be a good investment.
These are just some ideas and i'm sure everyone will have something good to share. I hope this was inspiring or helpful somewhat
. Good luck,
-side note: unless you want to change to carburetion, a BOSS 302, which is has cleveland heads would probably not do very well in your daily driver criteria.
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previous name: 84stangLX
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT