PP,
The current Tucker newsletter (October, 2019) has some more photos on page 5, but no more details. Here's a link:
http://tuckersnocat.com/wp-content/uploads/2019/10/volume-11issue-10.pdf
If Tucker went to the time, trouble and expense to truly overhaul/restore the machine to include a professionally rebuilt engine, new clutch assembly with re-surfaced flywheel as well as disassembling, inspecting and reassembling the transmission, and transfer case, not to mention all new universal joints in the driveshafts, new hoses throughout, etc, etc, I would think they would say so. That's a lot of work and expense and helps in justifying the price.
That implies (by omission) they did none of the above. I'm assuming the 318 is original to the machine and therefore dates to 1970. Back then there was no such thing as unleaded gasoline and cylinder heads did not have hardened exhaust valve seats or improved exhaust valve materials. If the cylinder heads have not been reworked, I would anticipate that may be required. Even having someone else do the work it's still only $1K or so, but that would have been addressed in a proper restoration.
Looking at the photos, I'm wondering if what I'll call the the "side shields" (below the hood on each side) are missing - or perhaps they were not so equipped back then? The new exhaust pipe protruding from where I would expect to see the side shields seems odd...
It's hard to tell with certainty from the photos, but looking at the paint it does not appear to be a nice smooth, glossy finish, but rather somewhat flat in appearance. It may be the lighting is causing that look, I honestly don't know....
Lastly, a question for you. You mentioned having seen this machine first hand and passing on it. I recall a yellow 543 of roughly this vintage for sale on craigslist (in Washington State, I believe) for quite a while and priced at $15K. Is this that Tucker?