Which version was used by the British?
The British only used the M7, which had the Continental engine. The M7B1, which was based on the M4A3 chassis, saw fairly limited service as it was produced quite late in the war. By then the British had switched to the Sexton. As Sandsmodels pointed out, the Sexton is almost a totally different vehicle to the M7, as it was based on the Ram/Grizzly (even the bogies were actually a different design to those used on the M7). So it wouldn't be possible to provide the parts for both in the same kit.
Personally, I'd prefer a kit of the Sexton to go with my Rubicon Achilles. But the M7 would be far more versatile as a kit - apart from the US Army, it was used by the British, Canadians, and Free French, as well as the USMC. It could include optional parts for a Priest Kangaroo (not much needed). And maybe even include the M8 ammo trailer that was often seen towed by M7s.
