Leon,
Just because I don't have a sales record for Grigg doesn't mean they didn't at least try engines. My record is not 100% complete. It's pretty good, but there are a few holes. Also, Grigg may have obtained an engine from an intermediary. DeLuxe/Motorities bought quite a few engines, and they'd sell anything at all to anyone who'd buy it. Recently I've tracked three engines in the USA. Reputedly these were purchased by Indian for trial, but they were all sold through Wallace Engineering, a Glasgow firm who built agricultural equipment and did not build motorcycles. All things are possible.
JFerg