Hello, I also have a '76 530i that I have been driving for the past 26 years. These are basically trouble-free cars once you address all the weak points. The cooling system is one of those. You can take the radiator to a shop and they can remove one of the side tanks and rod it out. Once you do that, your temperature will be a lot cooler. Thermal reactors were another problem; they got so hot that they cracked the cylinder head. Best solution is to take them out and install a set of regular exhaust manifolds.
I did a 5 speed conversion on my car, so I still have a good 4 speed gearbox and driveshaft in my garage. I also have the factory manual, so if you need any one section in particular, I can send you a copy. Good luck with your project and post some pictures when you can. Carlos Rubio