Smokin gun hit it square . Rc injectors .,remap , maybe the tb mod . Assuming you have the the right heads cam exhaust it will get the job done .

Mine dyno'ed at 545 and 617 Tq not using my EMI thunder exhaust, used dry exhaust and muffler during test. Engine mild mild porting on the intake, cut top of runners off, opened up stock cast iron heads slightly, cut down valve guides, bored .030 by Young Perf. Don't know what the cam profile is, and he said the only way to get more is a larger TB. I need torque more then HP so we stuck with modified stock intake. Yours being a lighter boat the Holley EFI systems with Intake might be the way to go. Just my opinion

But mine is a 502

I believe I read on here that the 502 / 454 mag MPI intake stops flowing right around the 550 hp mark.

As stated, the mpi intake is a restriction, cut down top of runners, port match it, have it ported if possible (very hard to find anyone interested in porting one properly as there are LOOOONG runners that virtually nothing can reach), buy a bored out throttle body (I use one and have a spare if interested) and a remap will be necessary on ecu. The stock injectors on a mefi 3 will support 600 hp no problem, I hear the older mefi with the fat injectors flow less fuel, you might need to turn up fuel pressure. I made 700+ hp blown with stock injectors at 78 psi fuel pressure. I made 650 hp NA on my 540 using a modified mpi intake and bored throttle body and well over a 1000 hp boosted. Is it worth all the pizzing around, well thats another story, buy a good std intake set up for efi,fuel rails, a scorpion or fast throttle body and use your stock ecu and wiring harness is another route IF you have someone competent who can tune it on the water. Buy a holley efi set up if you want the least amount of trouble getting it tuned or just bolt on a traditional carb, intake and distributor if you want to get out cheap. IF yours is mefi3 the ecu, unmolested harness and intake IF not rotted in water crossovers are highly sought after and you could probably get enough out of them to buy a new carb, intake and distributor, fwiw, Smitty