From an ex ECi employee;
A1A = 2 impulse coupled magnetos, variable pitch
A1D = 1 impulse and 1 direct drive magneto, variable pitch
A2A = 2 impulse magnetos, fixed pitch
A4M = solid main crankshaft, fixed pitch only, 1 impulse and 1 direct drive magneto
It's unknown how Mattituck actually configured the engine but this may help by characteristics. There are other configurations than these but they primarily have to do with the crankshaft set up.