Hi, first let me say I really like your build! I'm currently building a '77 widebody and also have a BMW e30 M3 which I've highly modified and raced in NASA GTS.
I've also also run CFD (Computational Fluid Dynamics) on the car to get the best aero balance.
I see a number of water cooled 911 conversions routing the radiator discharge air under the car. This will produce front end lift to an already light front end and could create a dangerous situation similar to hydroplaning. On my race car I actually moved the radiators to the rear and have the front intercooler air routed out of the top of the hood (black hole in the pics). This significantly helped the overall aero balance with the wing in the rear.
Depending on how you want to use the car once done, you may want to investigate other options for the discharge air.