I originally started off down your road with my 540 many years ago. Did the whole extrude honed MPI intake, Iron Eagle heads, Marine Kinetics Cam, Precision Marine tune. It ran very strong and it took a lot of dicking around to get there. Everything on that stock motor was modified somehow. Long story short I blew up the short block, did some trading up for AFR heads, then realized the MPI was no longer feasible to compliment the package. Decided to toss MPI away and go to the Holley HP fuel injection. Best decision ever. Been down your road, got and already wore out the t-shirt. 700 hp is expensive from where you are at no matter which way you go. Easiest way to get that on MPI is with boost. I wanted to stay naturally aspirated. I was looking at mine the other day trying to count how many original and unaltered parts were left. Oil pan & windage tray, couple brackets, bell housing, engine mounts, power steering pump and cooler....and thats about it. Would I do it again? not with the MPI.

It all depends on where you want to be. If you are happy with 500 hp, you can stay with the MPI. Anything over that, don't waste the time. put that money towards parts that have the full capability and even room to upgrade later.

Whats the budget $$ and work backwards from there, do you want to spend 8K or more for two after market blocks, I built 540's out of my 502's and like the results, but I wasn't shooting for 700 hp,

Thank you spoke with him the other day wrote it down wrong didn't want to keep bothering him

Yes already came to the conclusion that mpi has to go now the question is to stroke or not to stroke and pros and cons.

No I am using my 502 blocks because already have to bore the one that I have out and need crank so figured I'm halfway there need crank pistons rings so add rods and I'm there

So whats the final bore size, Im running Callies cranks, H-beam rods, AFR 325 heads, Wiseco custom piston and Bobs cam's with the stock 500 EFI intakes with custom Smith ECM tune, you can build em cheaper but I wouldn't just my 2 cents, good luck

Well, consider this. You need pistons. Then you'll probably want to upgrade rods since it isnt much more than rebuilding your stock rods. Then you're left with your stock crank. Which, you can usually sell for around 200 bucks. A new 4.25 crank, will run you around 675ish for a 4340 style compstar, scat, etc. So you'll really out of pocket around 500 bucks, to upgrade this to a 540ci setup. Not terrible.

The stock heads IMO, arent worth rebuilding, esp if they are tired and or have some damage. A new set of heads will stomp those 1960's designed GM heads. So, you'll need heads, pushrods, rockers, a better oil pan, bigger oil coolers, and so on. Then you'll need to decide on what to do for induction. The MPI ****tt will need to go. You can do a single plane and a carb, or a holley EFI setup.

Taking your time on a build like this, and really thinking it out with the right components, 700hp is attainable. You're gonna have to figure the entire engine build out piece by piece on paper, before ordering anything.

I have a buddy who had a 33 power play. He had 509's bbc with brodix heads and intakes 10.1 compression and made 709 hp and about the same in tourque with a 950 quick fuel. It was a beautiful boat. He just sold a few weeks ago. The builder swears the hp came from the heads. I believe they were bb2's or 3's. I had a 502 stroked to a 540 and was not a big fan of the geometry of the pistons in a marine engine, unless it is in a 10.2 block. I would stick with the stock piston location. It allows you to spin more rpms which will take some of the load off of the bravo's. Don't get me wrong i had no issues with my stroked engine but if i would have thought about it a head of time i would not have stroked it. I also sent my mpi to az speed marine and opened up the intake runners however with the cam that was in it it always had a code stored for the map sensor and ran rich as hell. Every now and again i had to crack the throttle to get it to start.
I finally put a blower on it and made 825 hp on a 29 single engine and never hurt the stock bravo upper or imco lower

If your goal is 700HP without supercharging, pump gas and sub 6k rpm's, your wasting your time with the 502's.

Instead of emailing RMBuilder, do yourself a favor and call. It seems like you have some misguidance and obviously a lot of questions.

He will tell you what you need with no sugar coating. If you are looking for someone to say, yeh - that will work - but in reality it won't, then don't call him. He won't get involved in that - nor will most of us. Some will, and that will be the wrong way to go.