I think you are thinking about the so called "baby nailhead", the aluminum block 215 V8. The tooling for it was indeed sold to Rover in England and with a few changes used for years in their vehicles. Don't think Jag ever used it, or Rolls, they had their own engines. It wasn't really in the nailhead family, but it was a similar design and might have shared a few parts, but not many.
I think the only TH used on the real nailhead was the TH 400. Don't think they ever got the TH 350. I've never ran across a TH 400 with a BOP {BUICK, OLDS, PONTIAC} and Chevy pattern both, but they may have made them and I just never saw one. I have seen the TH 350 dual pattern ones however. I think they came about in the late 70's-early 80's when GM was doing away with branded engines, They used up what supply they had built then started putting "corporate" engines in, which was the small block Chevy. My Grandma had a Buick with a Chevy 350 in it. By changing the trans and going to the dual pattern, they didn't have to keep making transmissions to match the other bolt patterns, BOP in particular. For a while, you still had the option on the branded engine or the corporate engine, but it wasn't widely known or advertised, and when some owners found out their Buicks and Pontiacs had Chevy engines, they sued GM for some big bucks.