Quick version- modify intake and exhaust as needed to use a flange mounted good turbo, not gm's van/ hummer turbo.
Long version-get cozy...
To use the van turbo, you have to remove the camshaft and crank for cleaning. Sounds silly but, been there done that. The oil in and out of the turbo is the problem. You have to drill the oil port for the oil supply into the galley under the intake valley. Then drill a hole down to he area of the camshaft so that only half the drain hole penetrates to the cam. Now you need to mill out the recess in order to hold the uneven "figure 8" oring, or do what I did and buy blank stock of headgasket material, make gasket, then mill the surfaces of the middle intake manifold section to have proper height clearance. If you build a spacer block like the Russian guy (cant remember name at the moment) was going to do for the oil, then your better off to custom build up pipes, and intake manifold to deal with the turbo no longer fitting either exhaust or intake manifold.
I have truck heads and made studs for mounting the van intake. Buy grade 10 threaded rod, cut to length, bend and re-temper with heat, then cryo. Buy a couple of intake gasket sets, You will ruin 1 set learning to torque as the manifold now tightens at an angle to the head instead of into the head. I used plasti gauge to figure the most even tourque. Not excited about having to do this in the future for repairs, as each area needs different torque. P.I.T.A.
The van heads have the intake bolts at a different angle than truck heads because of the needed clearance for the 2 side manifolds of the 3 piece intake manifold. After having done it, I would do something different. A custom up pipe set up to a flange mount turbo like gm 8, ATT or hx40ii would be better. Making a modified intake and up pipes would be easier than doing the alterations for the oil. The expense of a gm6 center mount turbo mod is more than the other options. The only reason I went with this turbo is my truck is tight on space for any other options. I was considering, and think I made the wrong choice to not put my turbo on the roof and be able to use a much better turbo.
What is stopping you? Nothing. I was on a mission to make it work, and I did. Just know that it will take more $, and a lot more time. Part of my time was offset, because I wiped out my center cam bearing and had to be that far into it anyways. It was still a mistake, but I've made bigger ones. You need good fabrication skills, lathe, mill, welder (still have to modify the aluminum intake), and time to spend. About twice as long to just build custom exhaust and intake mods.
Look up the turbo set up banks did for the modified hmmwv set up. It's a t3 flange welded to custom y-pipe for input. Then custom down pipe. Oil supply came off original truck location for ops, and dumped into side of oilpan. Then a custom pipe to the lower intake truck manifold. A much better choice imo.
My thing is I am unwilling to do a body lift, or modify the windshields, and for a hummer, one of the two is a must. Given your options- no friggin way would I use this turbo again.
Good luck to ya.
