By the way, I recently stumbled across the Grieve while trying to solve OGB-254. I was debating whether to post it as a new puzzle when you beat me to it. 
That's exactly wht happened to me! It's the best way to find new puzzle subjects.
You've found what is a really obscure car, although there are several photographs on the internet. I don't think it's even mentioned in Georgano's Encyclopedia. The whole car was built from scratch, presumably even the 20hp 4-cylinder engine.
Well solved.
