I don't have experience with the Grosset starter but I do have a 1982 BMW. I replaced the original Bosch starter on it with a Valeo. The earlier Veleos were known to have the field magnets come loose in the housing, causing it to jam. That was fixed on later ones. I got one of the later ones. It lasted about 18 months and then gave up the ghost. I contacted EME (where I bought the Valeo) and decided to get their own version, which they claim is tougher. So far, so good. They also supply a Nippon Denso version. It's expensive but supposed to be very sturdy. So they have three alternatives for the BMW. I'm wondering if one of those could be adapted for your purpose, especially the EME version, which they claim to be the toughest of the three. It was also quite reasonably priced. Best of luck.
I'll stick with that chromed lever on the off side for as long as I am still able, artificial hip and knees notwithstanding.
I'll stick with that chromed lever on the off side for as long as I am still able, artificial hip and knees notwithstanding.