(Graham, I don’t think our philosophies on “what-iffing” are that dissimilar, just the direction of thought process to reach a similar result.)

If you draw the P-35 to P-47 analogy, then the family tree is P-35, AP-7A (racer), XP-41 are essentially the same; small step change to P-43; bigger jump to P-47. With the Reggianes, it’s Re2000, Re2001, Re2002 similar airframe, different engines; big step in development to Re2005. Bearing in mind that the Re2006 (DB603 with 1800hp at take-off) development (concept only) was based on an up-engined Re2005, a Griffon-engine isn’t totally out of question from power loading, though perhaps the physical size of Griffon compared to the smaller Diamler-Benz may have required more design effort.

What I’m curious about, is whether Reggiane or other Caproni-subsidiaries could have managed a production order of 300 Re2000s in a reasonable timeframe; or would license production in the UK have been an eventual requirement? I don’t think Reggiane would have had access to British or US military engines (apart from civil commercial varieties), so “what-if” development would have required a British or US design group input. (Even assuming Italy kept out of WW2 in 1940-41.)