JAP 2S and ALCON water pump

I am new to this hobby but been in engineering of different sorts all my working life
I recently acquired the combination at a local steam rally (cost me £20 - the guy had 2 and said he had no idea if either ran so I paid my money and made my choice).
Turns out it wasn't seized but also no spark. Further investigations showed the mag coil was faulty and replacements are expensive (if you can get them). seeing as I seldom clear out my workshop I found a Lucas 12volt car coil and condenser along with a gel cell alarm battery so jury rigged them to the points and got a nice fat spark. The darn runs (once I altered the timing cam to the correct position to give the points opening about 20deg BTDC )

I think I have identified the engine as a 1937 JAP2S
I have found the following numbers on the crankcase
2SLF
6210820B
19266F.

3 questions I have are
What oil goes in the sump?
Should there be a Head gasket?
Will I be OK running it on ordinary unleaded?

Use SAE 30 grade oil in the sump. Some 2a/2s engine's have a steel shim headgasket and some have none, if compression is low a smear of Hylomar or similar on the head face usually seals them ok. Unleaded fuel will be fine. Enjoy your engine, I have had a few small Jap's myself and have an Alcon pumpset in pieces that I found buried in a hedge!

Pete.

This what we use in all our Villiers engines

http://www.screwfix.com/p/no-nonsense-hp-141-1ltr-4-stroke-engine-oil/96875