Can some one please give me input. I have twin stock 1991 502 mag 410HP w/b1 drives 1.36. The engines are low hours so I am going to do the top ends only. Does any one have a suggestion for Carb, Manifold, Cam, Heads, Exhaust package. The best bang for the buck is what I'm looking for.

Thanks!

Try And Find Some Used Hp500 Stuff

Building HP500 clones is a good suggestion.

But what are your goals?
What is your budget?

Exhaust $1500 and up - I like Stainless Marine.
New Heads $1500 and up - Edelbrock large ovals are good for a low $$ option.
Intake - Edelbrock Airgap or Dart
Cam - If you go roller, Crane 731
Carb - Holley 800 like on the HP500s

If you are pulling the engines to make a cam change, I'd do rings, bearings, and an oil pump too...

Like Pat said, goals and budget first.

Someone told me once that a 502 mag comes with rectagular port heads from the factory. Is that true?

True, and there are the same castings as on a HP500.

If the head castings are good, they could be rebuilt with the good stuff for about 2/3 the $$ of the new Edelbrocks.
The stock Merc intake can also be reused with the addition of an open spacer/adapter for the Holley carb.

The stock Merc 500 intake is a Dart single plane. It is a good one and can be found used easy and cheap. The carb is a Holley 800 DP. I would use the new HP 525 cam. Don't remember the grind but it is from Crane.

a like new 800 Holley for sale ....

http://forums.boatfreaks.org/showthr...ed=1#post82363

Thanks everyone , I'm looking for 500++ HP so the HP 500 clone sounds good! What about PatriYacht's suggestion of the HP525 cam?
I'm in salt all the time, Which are better options iron heads or anodized aluminum? And what is the diff between oval and rectangular port heads?