Actually, from reading Hogg some time back, we actually produced a quantity of 6pdr APCR. This never seems to have been used - and seems to be the HVAP ammo the USA towed AT (which were poor relations of the mech TD) recieved as reversed lend-lease.
6pdr APDS was never officially supplied to the USA, but was likely
unofficially traded for a few C-rations etc
Cheers
Andy