Gosh, now you've given me yet another reason to wish I still had my '81 Pickup and '86 GLI.
Anyway, I have no info but a couple of suggestions. One is to find a repair manual -- perhaps at a local library -- specific to Mk1 and Mk2 Golfs. Those things sometimes supply stats like dimensions and the lock-to-lock figures you want.
Another is to go to a reputable VW repair shop. I don't know where in Maryland you are, but I've been going to Desmond's in Parkville (Balto. Co.) since 1988. Give them a call. If they can't help you directly, they might be able to point you in the right direction. Rick and Phil's in Essex (also Balto. Co.) enjoys a good reputation as well.
You said OEM, so this suggestion may be unwanted. I would check into places which make racks for racing applications. When I was looking to buy a '75 Super, I had found two or three places nationally which
may have made racks I could have used.
I will check this weekend to see if I still have that info. I'm afraid the buying of my '71 and the need to move stuff into storage (or the trash) when we had our house enlarged may have been the doom of those files. I was only in the preliminary stages of investigation, but it may be useful nevertheless. (I know now I selfishly wish I still have/had it since buying a '75 in a few years has re-emerged as a desire.)