Ok, getting back to your actual questions.
You can use 49-way joysticks if you use Mame analog+, they take 8 inputs each, since you have 4 of them that would make 32 inputs just for the joysticks. You would also have to use special cntlr files to use the 49-way joys in standard 8-way games.
The mid resolution monitor is also theoretically usable with certain video cards using a special cable and MSDOS. I haven't actually read about anyone who actually did it, but apparently it can work. Realize that only mid-res games will be "correct", and normal games will be stretched to fit. But on the plus side the vertical games should look awesome, because they pretty much will be running at the correct resolution.
You might want to try posting a message to rec.games.video.arcade.marketplace offering to trade your Dark Legacy machine for a Mame cabinet. You might get several replies, you might not.
Many games shipped new with older monitors, it is not at all strange to crack open a game and find out the monitor is a year or two older than the game. The monitor tube got made by the tube manufacturer, then the monitor chassis got made, then they got assembled by the manufacturer, then it sat in their warehouse until the game company made a big order, then it sat in the game companies warehouse until it actually got put in a game. That time can add up to much later than any date sticker on the monitor.
Also many games get their monitors replaced and swapped around, so you never know if you have the original monitor or not.
To everyone looking for games, distributors and operators are the wrong places to look. Most of them don't have crap anymore. The places to get them are other collectors, classified advertisements, auctions, and game resellers.
For other collectors look on rgvac, klov.com, and here (in that order). Use google to search RGVAC for the name of your city or state, then contact posters who live in your area to see if they have anything or know anyone who does.
Check the local classified ads everyday. Games usually pop up pretty regularly.
Not every place gets arcade auctions, but many places do. So go if you can.
To locate game resellers search ebay for local games, and see if anyone in your area is selling more than one. Contact the people who have multiple games for sale, and see what else they have. Those guys usually have tons of stuff, and often don't want to deal with dead conversions because they aren't worth the labor involved in fixing them. Dead conversions are perfect for Mame.