This is a transitionary model between the early version (with flat base and brass engine frame) and the later version (with raised base and pressed steel engine frame). This version has the earlier flat base but the later pressed frame. It also has a mazac flywheel which dates it to 1953. (It was produced from 1950 - 52 with a brass flywheel.)
The SE2 was interesting in that it had the throttle situated in the engine exhaust. I know of no particular advantage of this design feature and, indeed, the idea didn't last into the next generation. The boiler is 1 3/4" dia x 4 7/8" long. It has the 3/8" safety valve and a standard lever operated whistle. The fitting for the steam feed pipe leaks a touch but not so much as to affect performance. Interestingly, the Tommy Bar on the overflow plug is painted red. I assume this is original as the rest of the paintwork appears to be original.
The feed pipe goes under the boiler in traditional Mamod fashion (to provide some superheating) and then directly to the cylinder. It has no lubricator or reverser. The throttle is built into the cylinder mounting block on the exhaust side. The single acting oscillating cylinder is 5/16" dia x 3/4" stroke. The exhaust is fed, as usual, to the base of the chimney.