From my searching, it seems like it is a fairly common thing to flip the throttle body from the factory side of the M30 intake manifold to the other side of the manifold, especially in a forced induction application, to allow better intake piping routing for an intercooler. There seems to be several methods that I have seen people do, including welding the throttle body straight to the manifold, using a spacer plate that is welded to the manifold, etc. Also, E28goodies.com sells a plate kit (https://e28goodies.com/product/%d0%bc30 ... plate-kit/) that appears to be meant to be welded on to the manifold (plus a blanking plate to cover the factory opening), but I haven't found anyone with any experience with that kit.
So I am investigating different methods of doing this myself, with the possible plan to design a plate kit (or something) that can be made and sold in the US. So any input from anyone who has done this would be great.
So far, to make the fit clean and sexy, I slapped together a jig to hold the manifold level in the mill, and programed in a flat cut to set the TB on:
Here it is with the flat and the TB air hole (pic taken before mounting bolt holes were drilled):
So far the plan is to machine a spacer plate with thru holes, as the TB doesn't sit nicely in that milled section, as protrusions from the TB interfere with the rest of the casting of the intake manifold. I will see how it works to run bolts through the inside of the intake out thru the spacer and thru the TB and with nuts on the outside. Access to insert and hold the bolts should be easy through the factory TB opening. I plan to use lock nuts or jamb nuts, maybe with thread lock as well to prevent the nuts from backing off the bolts, but I figure the risk of a nut backing all the way off and a bolt falling into the throttle body is very small, especially with the nuts visible from the outside.