Well, when I had all those issues with the E34, I seriously considered swapping out the H31 Hydro system for a vacuum type system.
Had a look at the 1 series master and booster. Its small and really compact, all you would have to do is apply a vacuum force (the H31 was fully hydraulic from the power steering, so no vacuum) and make sure that you can attach pedel mechanics to it.
Luckaly I got my master rebuilt (12k from BMW for a new one, R450 from david).
Its possible, guys have done it, its a lot easier as well with no ABS controller, so for an E30 project, why the hell not, the vacuum booster is about the width of my hand, maybe a little bit bigger, but nice for projects with no space in the engine compartment