I would love to play with a modern engine after the style of the K3...
Shorter stroke, of course, about 1,000 to 1,300cc in capacity, inline six, SOHC or DOHC, and intended for a car rather than a bike.
I must have a K3 pic here somewhere... oh yeah, Vennermark's at Lobethal in 1940:

Warren... please e.mail me...
r@ybell.net or raybell@racingphoenix.com