This is a Napier (American Napier?) Touring by Pettingell from Amesbury.
Yes, this is the answer I was looking for. I'm sorry if my previous reply "partly" was a bit vague. I have no idea whether this was an imported British chassis, or one made in the US, but the latter is obviously more likely.
I have no further information about the engine size or date of manufacture.
Joao gets the point.