Has anyone put Gen IV heads on a Gen V block without a water leak problem? I have a set of #781's I want to put on a Gen V block, but it appears that the water holes above the #2 & #7 cylinders don't have enough sealing surface with these heads.

Does anyone have a set of Gen V rect port heads?

you will need felpro #1047 head gasket for 4.500 bore &up 1037 for 4.250 + I also have several sets of heads new and used if you need them. Call Gary @513-561-4849

it will work with the felpro gaskets but you need to use studs instead of bolts to get a better torque on the heads

I am getting ready to do the same thing and here is what I was told by my machine shop. Mark IV heads will work on a Gen V block with the Gen V gaskets. However Gen V heads will not work on a Mark VI block. If anyone knows any different let me know before I try it. All I need is another breakdown.

I had a situation where I was going the other way around... I.E. Gen VI heads on a Mark IV block. I called the tech support at both Fel Pro ( Federal Mogul ) and Cometic... Cometic spent a great deal of time with me ( they were great ) in the end, they did not have a gasket recommendation... Fel Pro did recommend the 1037 / 1047 ( depending on std. bore vs overbore ) and stated that they have had good results either way, I.E. mark IV 's on gen 5 and 6 and vice versa. I upgraded my Mark IV ( 454 / 365 hp magnums ) to be identical to the HP-500...and topped it off with Gen VI heads. I had water problems in the oil. Blamed the heads at 1st. It turned out to be reversion. I pressure checked the head/block combination and they held good pressure. I was uncomfortable with the reversion problem aggravated by the low velocity square port heads, requiring 800 or better idle, and thus I am going with the 781 oval ports. When I 1st suspected a problem, many folks have quite different opionions about wether or not it can be done.
For the potential problems.... It is best not to mix and match. The trouble that CAN result... is too frustrating.