The F class was very similar to the A class except for the saddle tank. The F class is one of the trickier ones to sketch out, because there were several different batches from builders, and variations between the batches, front overhang for example, definitely existed. There are two styles of foot plate valance too. The first five at least had a straight valance, the remainder curved as drawn.
This second sketch shows a lightly swindonised version of the F class, still with the Barry boiler and bunker, but GWR safety valves and cover and several other standard Swindon fittings.
Edited by JimC
Now in colour. Added the GWR version of the saddle tank.