get some 1/2" thick steel and cut your own flanges. I used 98 T/A stock stamped stainless manifolds, they fit really tight to the block and transmission. I also used truck manifolds without much issue before. If you can wait, NITROUS is developing some long tube headers for the OBS trucks and they may fit your application but they were designed for the 2WD trucks since he had one handy to test fit/build the first set on.