@Runner
Probably yes, as Samo says straight 30wt without a filter. I am using straight 30 in my filterless Dursley and a detergent multi-grade in my filtered Listeroid. Really though, I would bet it makes little difference given that modern oils are so much better than the original oils available when these things were designed. Frequent oil changes are the important part.
Thermostat....we used to have one in the listeroid (with a small hole to allow for air to purge itself out. Since switching over from a large capacity cooling tank to a cast iron radiator, I found that the 'stat is not necessary in my case.. It all heats up quite quickly and maintains a good hot temperature without overheating on an average 2 hour run.
As for a water pump, also not necessary.....if you can arrange it, a thermosiphon works just great with no moving parts to fail.
And of course, before you run it, do take it completely down and clean it internally. Set it up properly.....bump clearance and timing will make a big difference in ease of starting. You will know your engine and be confident to make any repairs and adjustments. There is lots of good information on setting up on the forum; poke around through past posts and you will learn a lot.
I am an off-gridder and use my engines to provide power when the sun does not and also to power up my shop.
We are off the beaten path, my "machine shop" is little more than a collection of hammers and files.......goes along with my skill level.........That said, I have gotten good reliable service from my Listeroid over the last 5 years and refurbished a non-running Startomatic 6/1 that is now in my wood shop.......thanks to all the help and advice I have gleaned from others on this forum. Thank you all!
And Runner.....most importantly, have fun with it!
Cheers,
Hugh