I got a couple heads from a 1989 R100GS for the salt racer. These are the ones to have since they have the so-called ‘D ports’ and have larger intake spigots since they take 40mm Bings. Got them cheap because one of them was busted up: 4 broken fins, a cracked 6mm hole that takes the rocker cover stud and a stripped spark plug thread. Other then that, they were OK!
Aside from the broken fins, you can see where I welded up the rocker cover hole ready to face and re-drill:
The process involves TIG welding a bead on top of the broken fin edge, then another bead on top, then another, then another….until a thin wall is built. Then into the mill to have the sides shaved to the correct thickness then another couple beads and repeat.
And after quite a few hours of welding, milling and filing: