A10, 1200's & a12's, including GX, have smaller valves [29 & 35mm]
A14 & A15 engines have larger valves [30 & 37mm]

The exhaust ports for all A series engines are square. [crzy_1200_ute was just geting a little crazy there for a moment]
Oval shaped inlet ports were used on 1200GX, A12GX, plus Aussie versions of the A14 & A15.
Round port heads were seen on A10, plus regular model 1200, & A12 & some versions of the A14 in some overseas markets.

A10 & 1200's have additional drillings for rocker oiling.