I've included a couple of shots of the underside of the chassis which I had taken prior to your link to the thread showing the difference in the chassis. I'll need to go back down to the shed and have another look, because I can't actually tell definitively from these photos (but maybe you or others can).
Interesting to hear that the discharge cover is homemade. It's a very nice job.
The other thing I notice is that the engine seems to sit atop lugs that are cast as part of the base, which doesn't seem to accord with the sheerline, four star or four stroke versions in the thread you directed me to, as far as the photos go, but the schematic does show one as having them.
Now I see that there probably was a much better area in which to post these sorts of queries. Apologies to all for my lack of forum etiquette/knowledge.
