Bill,
Actually Indian manufactured an inhouse(Springfield, MA) designed vertical twin and sold a very limited number of them along side their V-twins, just a few years before they ceased production in 1953. By the late 1940's, Indian management had seen the British brands starting to take a significant portion of their sales away and seeing the writing on the wall they knew they would have to update their line from the old flathead V-twins Chiefs and Scouts in order to compete with the British and Harley Davidson OHV engined motorcycles.
Unfortunately, the design was rushed into production and almost all of the vertical-twins had major reliability problems and with the tremendous amount of warranty work that had to be provided, it ultimately sullied their reputation and forced Indian into bankruptcy.
A few years after they shuttered their Springfield plant, the holding company which then owned the name "Indian Motorcycles", did import Royal Infields twins rebadged as Indians in a short-lived effort to revive the brand, but as you know that lasted only a few years with little sales also.
I read somewhere recently(however, I can't remember from which publication) that there was a last-ditch effort, sometime in the early 1950s, to use Vincent engines in Indians, but the companies involved could not reach an accord, so it never came to be.
I think that would have been an interesting combination, but of course it would have been a very expensive bike to purchase.
Cheers,
Dwight
(and gentlemen...don't forget that there was a Ducati vertical-twin....the Tornado, of the mid-to-late 1970s)
