I have read http://www.nastyz28.com/ubb/Forum5/HTML/013017.html and it looks like it might work with a special gasket, or not.

A friend of mine has found a good deal on some gen 5 heads and asked if they would work on his older block. Being a small block guy, I don't have a clue.

You can use Mark IV heads on a Gen. V block with special plugs for the water jacket openings in the block (different sizing/shape to them)- so I would think the reverse is also do-able (putting plugs in the Gen V heads to have holes match).

One thing to note, however, going with Gen V heads may not be much of an improvement if a high-lift cam is going to be used- the Gen V heads have a "set" valvetrain- i.e. no rocker adjustment- so this has to be modified if going to any cam with a bit more lift than stock. Also- unless the Gen V heads being used are HO heads (crate engine or over-the-counter performance units with larger valves)- they're just peanut port heads anyways and have no huge advantage over any Mark IV head.