Any way to know if it was a Vietnam recon tractor? I'm not really sure what that even is lol. The head gasket has been reused before as well as literally every other gasket on this.
Gaskets re-used strongly suggests that origin!
10~20 years ago before Yanmar-USA sued importers to halt importation of used tractors, there were two primary sources here for YM2000 and other models originally sold to the Japan domestic market:
1) Used tractors from Japan. Their tax laws encourage replacement long before a Yanmar is worn out. And the trade-ins there are near-valueless locally (tax law, and a culture valuing new) so a strong export market began, to ship out these good used tractors at a time when family one-tractor farming there was declining. Just ordinary used-equipment exporting.
Then 2): currency exchange rates changed and the exporters ran out of good trade-ins so prices rose. A new market appeared: shops in VN that rebuilt tractors that had a first life in Japan then were run in VN until they wouldn't run any more. Some of these gorgeous repainted 'rebuilts' were 'Frankensteinmars' assembled out of unidentified and unrelated parts.
One former US importer who chose his own imports personally in Japan said he saw literal junk tractor components jammed into ocean containers to go to VN, for parts to build the Frankensteinmars. He said they might as well stand the container on end and pour in the junk assemblies - disassembled transmissions, disassembled engines, etc. - all going to the VN rebuild shops. There is no legal access in VN to buy genuine Yanmar parts for these rebuilds. So everything that comes from the VN rebuilders is made from used stuff or at best third-party parts. Worst case, parts where they handed some kid a file and a block of steel and told him to fabricate something that was unobtainable. With no model to work from.
So a VN rebuild is a gamble. Most people came out ok ... But - I often visited a US branch owned by one of those VN rebuilders that wholesaled 200-400 rebuilts per month (according to them). Long story short, the individuals running it were honest and got buried by so many warranty returns that they made good on, that it bankrupted them. I recall the manager said her brother went back to VN to plead for better quality shipped over but that didn't help. They simply disappeared one day.
A real Yanmar tractor is excellent, near indestructible, even if its old. A VN rebuilt can have its own personality - some good, some not so good.
If I'm reading your posts correctly it seems you have an engine originally from one series (YM1900?) in a later (YM2000) series tractor. Or maybe somebody hung YM2000 sheet metal on a YM1900. In any case its maintainable, just a little confusing to find the right parts.