Shortround6
Major General
As an aircooled engine, going from 24 to 32 cylinders was not a big deal - needed new crank, new sleeve drives, new crankcase, but the cylinders, sleeves, heads, rods should all be the same.
R-4360 used the same cylinders (or started with) as an R-2800, work started in 1940. P&W pitched to it General Arnold saying they could develop it in time for the war, unlike the sleeve valve projects they were working on. It barely made the war and had a rather notorious reputation for reliability and maintenance woes in it's early years.