Okay, I just found your other thread and can offer a few suggestions...
These websites are going to be your friend for race parts:
Ireland Engineering
Turner Motorsport
Pelican Parts
Any BMW owner needs this site bookmarked for the awesome diagrams and part # cross-referencing:
Real OEM BMW
If $5k is your budget, you have some room to play. Try to find a later M40 (16v I4) or M50 (24v I6) engine with the later 4-speed auto attached. Like Wilber, I have no idea if it will be any stronger, but at least you'd get an extra gear. Either way, add a heavy duty trans cooler, and put some Redline synthetic fluid in it right away, and it might go the distance for you. I don't know of any shift kits available out there, but they could exist.
Do all the suspension bushings (pick your favorite material, it's out there for the E30), then drive it and tune from there. As said above, SS lines are always a good investment. Maybe convert to rear disc brakes? I would do wheels and tires before any other suspension stuff, E30's are pretty tossable and neutral from the factory when everything is fresh.
If you really want to stick with the M10, or just have a boner for the "old-school way" like I do (I'm currently building an antiquated Subaru EA82 to period WRC spec with a bunch of rare low-production parts) there is power to be had, but it won't be cheap. Look into Schrick cams, and send the head off for a major work-over. Get some 9.5:1 compression pistons, then slap it together and make the next big decision - you could run carbs, ITBs, or even standalone EFI at this point. THEN a header, full exhaust, and good intake will make a hell of a difference. It will sound totally awesome too. This setup will net you somewhere around 170HP, and be period correct. Not your only option, but certainly one way to go.
Good luck with the project, now that I've seen your other thread everything makes a lot more sense to me.