Figured I should put some closure on this just in case it can help someone else:
So I decided to put my money where my mouth was and buy the cheapest ignition lock I could find. Got one on ebay for 10 bucks. Quality was actually very good and appeared equivalent and externally identical to the original Mopar. However when it came time to swap over the "sidebars" from my original lock into the new lock to match my key it didn't work. Either the slightly different design of the sidebars or an actual internal difference somewhere inside the lock meant that they were not compatible. I toyed with the idea of buying a second $10 lock which would hopefully have provided me with a big enough selection of the sidebars that I could have placed them in the correct places to get it to work with my key. There was a bit of risk there - a) the 2nd lock might not have come with the needed selection of sidebars (I'm about 95% sure it would have though) or b) there might indeed have been an internal difference in the new vs original locks which could have had me trying who knows how many combinations of sidebar positions - there would likely be a logical way to figure it out though but I decided to abandon the dirt cheap route and go with something I was sure would work.
So I found a new "OEM" lock with keys on ebay for like $39 that I thought I'd buy and swap my original sidebars into. Nowhere on the listing did it say "Mopar" but the guy (a locksmith) assured me it was the same as Mopar - I assume it came from the original supplier to Mopar? After asking some questions he told me he had a lock kit without keys that was designed to set up for your original keys so he made a special listing for me at the same price. Anyway, got it in the mail this morning. Looks the same as the Mopar with some subtle differences (there is a little plastic nub that's black, not white like my original) - it was completely disassembled in about 7 individual baggies and came with 5 each of the 4 different possible sizes of sidebar (they are stamped with either 1, 2, 3 or 4) and a little pouch of lock grease. Another baggie had 10 of the sidebar springs (you need 8) and another had the little rods and springs that fix the lock in whatever spot you turn the key to. There were NO instructions though so I think this kit is targeted at locksmiths only. I had sketched the locations and numbers of sidebars from my original lock last time I had it apart so I assembled the new lock the same way (the original lock sidebars were stamped C1, C2, C3 and C4). It worked perfectly on my kitchen table and also works perfectly in the ignition.
So summing up - I think the final solution here is the best way to go. I bet getting a new OEM style lock with keys would work just fine and you just swap in your original sidebars but I suppose there is some risk that your existing sidebars are too worn and might cause issues. The work is kinda fiddly and takes some organization and care but anyone with mechanical aptitude and some attention to detail could easily do it. Have a clean work area, good light, reading glasses if you're as old as me and whatever you do keep track of which sidebar comes out of which location on your original lock - get those mixed up and you're screwed and will have a very expensive bill at the dealership or locksmith.
For instructions you can go to that video from Rock Auto I mentioned in a previous post or you can probably find something on Youtube.