I did have the same thought if it was a compound due to the valve on the top inlet, but both cylinders are the same size and the pipework would be 'interesting' to take it from the exhaust of the top cylinder to the inlet of the other. The little oiler on the top came with a box of other bits and pieces which had nothing to do with this engine, but oiler looked right and fitted, so there its going to live for evermore!

I did also notice that the bottom cylinder has a few remaining pieces of wooden lagging on it, but I think for this engine the naked cylinders look quite good

It's a bad time of year for ordering things online.  Volume up, and lots of temporary help filling the halls at Amazon and UPS depots.  A present for the wife got here about 4 days later than promised (but luckily before she came back from a trip to her mother's house, so I was able to get it safely tucked away before she saw the rather obvious return address), and nicely crushed, and well dampened from our persistent rain...so much for the extra money spent for gift wrapping. 

Maybe some day you will revisit this, Paul. Why not? The concept is (to me) sound. Just the details, maybe. I think your piston is too heavy. Make a new one? Make it shorter, and aluminum. Get rid of the ported exhaust and simpler, just uniflow it.

Here's a very crude pic, where I mangled yours -- just a schematic, not to scale (especially the gross unflow port(s) I hamfisted in here, or working chamber volume and timing. The devil is always in the details, but stick with it and you will make it work -- er that's my belief anyway!

(btw.....ya kin always plug holeses, ya know...)

With all the clocks ticking away, its put the shop elves to sleep...  Dreaming of new tools, counting sheep jumping over Bridgeports...  beer trucks making deliveries...   

Very interesting  engine!  Where do you find all these old models?!