Cujet, Listeroid values are all over the place. I have watched both used and new ones sell VERY cheap at auctions and have had a few through the shop that the owners had a tidy investment in by the time they paid my bill. With India price increases, currency exchange and freight charges an India engine gets very expensive. It is cheaper to import a good CS Lister than a Listeroid, the only reason to do that now would be if one wanted the higher HP versions that India offers,, in my opinion.

Hi, I am not familiar with that brand but usually, (stress usually) that style head will be brushless and internally regulated and outside of burnt windings little goes wrong with them but when left to sit for a very long time they will lose the residual magnatism they need to power up which can be restored with an ordinary electric drill. If you know how to wire it for 110 output temporary a receptical. Plug a drill in pull the trigger and spin it backwards. Some report results spinning with fingers but I've had better luck with two drills. One plugged in to the generator and spin it with another drill via a rod chucked in both. it can also be done with a 12v battery but somebody better schooled than me will have to tell you how to do it that way. They also have to be nearly up to speed to start generating,, half speed won't do it.

Try Master's farm supply in FLa. Several years ago they bought out one of larger importers supply of parts. They ARE old stock and may be weathered but I have never gotten anything that was unusable.
https://mastersfarmsupply.com/

The ban on small diesels has zero to do with being dangerous. They could not meet tier 3 or 4 emissions.

What are you calling a Lister and where are you? To me and most others a Lister means it was built by RA Lister in England. India built engines are normally called Listeroids and are considerably less valued by most people.  Back to your question. RA Lister built CS engines that are rebuilt and ready to use will bring $3,000 dollars ever day of the week here in tbe USA. In europe where they are thick on the ground they don't bring 1/4 of that. The other thing that is missing is freight, duties and other fees that are tacked on before it reaches your door. Door to door single engine import costs to USA from India are now in the $1500 range thus there is a considerable difference in cost for an engine here and one that can be picked up at the back door of the erection shop

It's been a while since I have had the guides out of a CS head  as I repair the old ones in place. That being said I do believe that both bores are threaded  as the valves switch positions on the number 2 side of a twin. I have two older 10/2 with wet injectors in the line for rebuild but it will be a few months before they get in the shop. You are correct that the longer couterbored guide is used to prevent sticking of the exhaust valve.  Replace the guides as they are now. 

Agreed, I didn't intend to cast away the thought of using WMO as engine fuel but there is a lot of work to it, seemingly. Some of the home brew refinery ideas are pretty scary!
 Low cost solar has just about put a stop to other off grid technologies.

There are flushing products available that you add to the old oil and run the engine a few minutes and drain. Any automotive parts store will have it.  If there is doubt about prior maintenance being done I would take the time to pull the 4 bolts out of the crankcase door and take a peek inside. I have had a few neglected LDs and SLs in the shop and the gunk in the crankcase was DEEP! A gallon of kerosene and a few minutes brushing got the worst out followed by a couple quick oil changes.