I made 650+ hp NA at one time from a 8.4-1 540 w mpi manifold, and 1115 hp with boost blowing thru same intake. I made 560+ hp recently from that same modified intake w 8.7-1 502 with iron heads with slight port clean up work, bored throttle body, hp500efi cam, right air cleaner/flame arrestor and lots of dyno tuning on 89 octane, talked to 100+ people in past 10 years on the 502 mods, conversation usually ends when subject comes up that aftermarket exhaust is needed to see much gains other wise very limited on cam choice as far as reversion. NO MAGIC BULLET that will give a 502 mpi a measurable gain with stock cam, throttle body, heads and exhaust. TPIS sells best stock throttle body mod out there for 502 under 300$ Much cheaper and easier to buy cheapest open plenum intake and imported throttle body if your going after strictly high rpm hp, mefi can easily be used to control it still. On my up coming dyno project I am using a imported intake I bought on ebay with fuel rails under 200$ and a giant throttle body that cost 220$ as a baseline THEN bolting on a 500 efi intake that will be modded in stages to see IF I can make close hp and more tq.

Cheap throttle body

Modded intake pics

OK so you were just shortening the runners till they met plenum floor, very slight change in power band due to runner length

When you made 560 with iron heads you talking the stock ones cleaned up or aftrmarket iron?

http://www.enginebuildermag.com/2008...-mild-to-wild/

Pretty cheap to knock a good 1/2 inch or so off the runner length and fix the throttle body if your adding cam and exhaust for that 500+ hp thats in there. Made suprising power on a 540 for me
Still a ugly sob though , imo.
That gen 5 mefi now runs rc injectors on a cutler intake and throttle body. Never got to try the 2 efi syztems back to back unfortunatly, but looks way better. The cutler is similar in outside dimensions to the ole hp500 carb dart intake , maybe a skosh more volume.

Pocket ported/bowl blended a set of new 088s i got cheap bare, put a set of used inconel valves in exhaust i had laying around, proflow stainless intake valves from comp products, intake had a lot of porting, previosly made 650 hp on a low compression 540 w afr cncd heads and big cam, bored out throttle body, also made over 1100 hp blowing thru that intake w procharger on same 540 w bob m cam, fwiw, Smitty

Your dyno testing made my old gen 5 502mag flame arrestors had laying around double in value overnite.
Beer is on me if your ever by lake lewisville. Always wanted to compare the stock 502 efi ,modded then the cutler back to back same day but it never came to be