MK IV, GEN V, Gen VI

I would like to know specifically what the compatability is for the MK IV and Gen Vi. I am very aware of the Gen V headache as I have one in a ski boat that is finding a new home this winter in favor of the 496 MK IV stroker I built for my truck. I have a GEN VI that I would like to put MK IV cast heads on for towing and am under perhaps the mistaken impression that the 80's '781 casting oval ports will work on that block. I am using a 4L80E tranny with a box so the GEN VI block makes sense for ease of mating up to the tranny.

I have read a common opinion that says stay within the late model or early model parts. I see that most all aftermarket aluminum heads fit everything with the right gaskets. I also read that the problem with the GEN V is largely lack of compatability with anything, much less itself. I have another set of 781's with 2.06 intakes that I would really like to use for towing and intake manifold considerations. Not a big fan of aluminum for extended pulls. Anybody done this with success??

old head s will not seal up on the mark 5/6 blocks this has nothing to do with the right head gasket there is no iron on the older mark 4 heads to seal them up on the newer 5/6 blocks .the alum heads will as they made the the deck of the new heads to fit both engines BUT not old GM ALUM heads .i mix parts from all bbc over the years. some parts just will not work no matter how much machine work you willing to do.. .the new mark 5/6 heads will work on the older mark 4 block as a wider deck and seals up fine with the rigth gaskets a 5/6 head gasket and some block prep work on the deck by drilling two added water holes 5/8 in the deck all older bowties mark 4s have this done its lets more water move anround the EX side of the head .some blocks have two of the lower deck holes in the block some older blocks have only one .when i rebuild a bbc most of the time i drill the deck all gaskets have the lower holes in the head gasket .the only mark6 block that a older head s OEM will fit is a CNC bow tie as GM closed up the open deck thats on the 5/6 deck in OEM form as for race use some do not care much for the open deck of the 5/6 deck heres the hybrid deck on the CNC bow tie block

So having said that, the GenVI I have was done in late 99 by the casting number so it probably came out of a 2000 truck of some sort. It has something other than peanut size ports which I assume are the standard port size for a Vortec. What is the difference between the standard oval port intake and the Vortech oval port intake? I will be using a carburetor so intakes for a Vortec seem to be a little limited. Not looking for anymore than 5500rpm so those ports look like they will do a good job up to the 5000rpm range for me, not looking for a cam that goes much above 5200 anyway.