For which bike are these cylinders?

[pkrpkr]

Can anyone help identifying two sidevalve cylinders I have found? The piston diameter is approx. 70mm so I presume about 500-600cc on a twin.

Thanks,
Peter

[Darryl.Richman]

Because of the 6 crankcase mounting bolt holes and the shape of the cutout over the valve area, these are for the side valves in the models from 1937-1942. That includes the R71, R61 and R6. But only the R6 https://vintagebmw.org/model-lookup/?shownode=6337 and R61 https://vintagebmw.org/model-lookup/?shownode=6999 have 700mm bore pistons.

[pkrpkr]

Thanks Darryl!