If it is of interest, I have just put Magnum heads on my 360. I mention it because I think it has got to be the cheapest upgrade by quite a margin.
They definitely flow better in stock form and with a 20 thou gasket you get about a one point increase in compression. I did port mine a bit first but nothing radical, took me one afternoon. I'm pleased with the way they run, noticeably better than the stock 360 ones that were on there before and it uses less fuel too (I actually had to go leaner on the carb. !).
I believe the stock Magnum heads are dirt cheap to buy over there because everyone says they crack. This is true but there is a school of thought that it doesn't matter (I think I read about that on the Abodies forum).
The cracks that develop are very fine hairline between the two valve seats. They don't go near the water and when the valves are closed there is only about 1 mm of the crack showing (so it's like less than the gaps on your piston rings).
Anyway, my heads did have a couple of cracks but I used them just the same and there was nothing to see on a compression test and they run fine, so I guess that proves it (for the time being). I have another set with no cracks but they are on my rebuilt Magnum motor which is waiting to go in, so this was really a bit of an experiment in the meantime.
The only thing I had to buy was different pushrods (my engine already had pushrod oiling lifters, most aftermarket lifters are like that). I got some push rods listed for a 302 Boss Mustang which were spot on the right length.
The two main problems with using Magnum heads is the stock springs are quite weak and the valve spring retainers hit the stem seals at about .52 lift. Since my cam is pretty mild it's not a problem on these heads, but you also have to factor in that the Magnum rockers are 1.6 ratio so they do give you a bit extra lift.
With the Magnum heads on my other engine I have a bigger cam and I had to cut the valve guides down and use tougher springs - that does get expensive (the springs I mean).
