pacifichistorian
Banned
I'd say (unless the timing's way off) start with M3 Lee/Grant running gear & add Chrysler multibank engine, & design for 6pdr with an option to fit 17pdr later. Given the lathes for 57mm exist, & given there are some fairly obsolete 75mm/3" around, couple the breech mechanisms of these with 57mm bbls (as the U.S. did, IIRC, with the 3"), improve the power of the ammo, & put the 17pdr on the front burner; install the better 17pdr as it begins entering service. To do this, tho, requires not re-equipping with 2pdr AT (after heavy equipment losses at Dunkirk), so simply refit with 6pdr, instead... (You will probably need more Canadian
production to make that happen, tho.
)