So here's a wrap-up. Hopefully Matt/Gamefixer is lurking around here and can clean up my own comments with accurate and coherent helpful information for masses who might come across this thread later.
As noted in the beginning of this thread, when powered on at self test there were no errors showing on the segmented LED data display. The game had sound and appeared to play blind. However, there was no display appearing on the monitor at all except when a hard reset was done at the upper left corner of the RAM board. At that point I could force it to display an image like the first pic below. I couldn't tell if it was it a board problem, the dreaded data cable, the monitor, or all the above.
Gamefixer found the first issue. (I'd be curious if anyone had a good explanation). The ROM board in the cabinet was loaded with the twelve roms specifically marked "Joust" from the factory. Big problem though. The ROM board literally had no place for the two special Williams chips. I'm not saying they were missing -- I mean there was literally no spot on the board for it. See, Second pic. To my untrained eye it appears to me that that ROM board is completely original with nothing evidencing from the solder on the back that anything was added or modified.
Upon receiving my boards, Gamefixer sent me a pic comparing a known good Joust ROM board (center) with my specimen (left) and, for comparison, a Williams Defender ROM board (right). Clearly this looks more like the Defender Rom set -- but with all Joust ROM chips on it. (In case anyone has ever seen something like this before, there was an extra board provided in the purchase of the cab that looks to be a Williams board. Perhaps it did all the logic the special chips did?) In any event I fail to understand how the game could coin up blind and show no errors as it was when the two Special Chips were not there.
There did not appear to be any solution to that puzzle so Gamefixer gave me a very reasonable deal on a replacement ROM board he had laying around somewhere. For hardly more than the price of the parts, he did the lithium battery conversion and the conversion to the newer 4164 RAM to run on +5. With the ROM board swapped out and the mods done, everything was working on Gamefixer's bench better than new. Problem solved and now, for certain, no further display issue could be attributed to the boards.
Once, I got everything back I threw it back in the cabinet. I received the same garbled display. See, Pic 1. (Very much like the pics in #11 above. Now we definitely had a monitor problem. I'm no monitor expert, but the image you see in the pic is exactly what you'd see on the screen in person, meaning specifically there was no rolling or movement on the screen at all with still images. I futzed around with L351 and turned it more than two full turns and suddenly got a correct display and reasonable picture. (Gamefixer previously called that one too earlier in this thread, with some modest change of a half to full turn in either direction I assumed I was on the wrong path of the decision tree. Instead, it turn's out I just didn't go far enough to make the difference. With a reasonably good display and working boards, it's now worthy of dragging in the house. (Here in Ohio it's colder than a witch's something so it hasn't been thoroughly cleaned, etc. just yet until it gets inside). (I still have a couple of other small issues related to a elevated voltage thing, and some monitor display stuff I want more info on, but I'll see if it's in any other threads and will post separately with that question if necessary).
Lastly, a point of honorable mention. Gamefixer is a good dude and so far as I can tell is extremely knowledgable. As noted above, he tested everything and gave me a more than far price on the missing hardware I needed and couldn't just buy online. His work was fast, thorough and more than reasonably priced. I tried not to contact him much figuring I'd learn what I needed to know when I needed to know it -- but if I did send a PM or email he'd be back to me faster than my kids. Even with the time involved in sourcing parts, I still got my stuff back within a little over a week. I was impressed. All said and done, when I figure out this rep points stuff, he's deserving of something there too. (I never would have figured out that part of my ROM board was literally not there).
Hey Gamefixer, did I miss anything on the boards that should be further noted?