Hi again
I think I have figured out the problem for myself.
By pure chance (and the fact that I was looking at the older 1979-1981 games), each of the Mame ROMs I tried while setting up Recalbox only ever had a single set of controls.
Although the TAB menu includes and allows modification of P2 controls these are only for use when the DIP switch settings are for a C**ktail cabinet.
Looks like on earlier games I have to live with using a single set of controls!
Steven