I have two stock 502 MAG MPI's with 220 hours. I have a chance to purchase two new sets of aluminum heads at a great price. But it sounds too good to be true that I can just bolt on aluminum heads and get more power. Do I have to change timing, cam, exhaust, etc... to get any hp gains. Thanks.

yes aluminum heads make a difference
but it is a combination of things that will make the hp
bottom end ,cam,heads and intake

Depending on the head, how it flows and what compression ratio it ends up. Yes it can increase power quite a bit. Also maybe a 200# weight saving on a twin application.

Remember you get what you pay for, if its sounds to good there is a reason.
If they are an off brand you could spend more in machine work than they are worth. You need to find out what kind of valves are in them, what springs, what CC are they.
IMO enjoy what you have, changing heads on a stock engine will get you small gains and minimal increase in speed.

It is not so much that the heads are aluminum, as much as the weight savings. Also depending on the heads what makes the power is the style of head, port style, chambers etc...

Cam, intake, compression ratio, exhaust type, fuel system & overall cid all also have an impact on hp & tq.. Jamie / Lakeside

Merc did a lot of research before they used the heads that are on them now. If you are not changing everything you would be better of leaving it alone.

Agreed. Also, if you don't have closed cooling your asking for problems.

weight and ease of repair when there is a failure are the major advantages IMO.

What heads are you looking at? If you don't know what to look for, you may end up hurting your performance.

I thought Chevrolet did the R&D on the 502?