All is not as easy as it seems.
The HMMWV manifolds require a odd sized 2.618'' (about 2 and 5/8'') compressed doughnut/ball/mushroom gasket, not 2.5 inch like I had originally thought.
The part number for the HMMWV manifold gasket is:
EDIT the correct GM part number: 15035747 appears to be close enough
Data page for the real part.
http://www.dlis.dla.mil/webflis/pub/...9738&newpage=1
The GM parts web site says they can get it for $20.
I think that gasket will fit a 2.5 inch 6.5T OE style pipe close enough. If not I am sure I can make it fit.
The banks manifold does not use the OEM style gasket.
I believe it requires a 2'' header collector flange with a 2 inch pipe. I don't know where to get a 2 inch header style flange so I will just have to make one out of the old pipe.
EDIT: I was able to convert the OE style flange to a flat collector style flange very quicly with nothing more than a hammer and it looks really good.
I will hand cut a copper gasket for the banks since sourcing gaskets is proving to be very time consuming.
The cross over pipe is a little more than half way done, but I am out of good 2 inch pipe and I don't want to use the crinkle bent stuff they have at advanced auto and auto zone.