Dedicated MK1 cabinets are pretty rare, chances are really good that it is a conversion based on several things.
#1. This cabinet was usually converted, often multiple times.
#2. Being sold without the PCB. You are only going to get a cabinet minus PCB from either a collector or someone in the coin op industry. Home buyers don't take parts out before they sell them. If it was a dedicated cabinet, then the owner would likely just buy a boardset so he could get $400 for it instead of $100. Also related is buying a stripped cabinet. The only people who totally strip games are big time collectors and coin op industry guys. If they (who do this all day long, or do it for a living), didn't think the game was worth restoring when it was mostly complete, then it certainly isn't worth restoring now.
#3. Mortal Kombats, Street Fighters, and Tekkens are all often referred to by the name without the number by sellers. The mainstream collecting world (which is the main market for resellers of this stuff) doesn't care too much about these games, and thus the sellers don't tend to be as meticulous about them as they are early 80s games. So it may very well be a 2, 3, 4, or might not even be a Mortal Kombat in the first place.
#4. The size of the monitor doesn't really say much of anything when it comes to big name 90s games. Most classic cabinets will actually take a 25" monitor, and big conversion money earners like Mortal Kombat and Streetfighter would often get larger replacement monitors put in their old worn out cabinets.
Unfortunately the game PROBABLY also has a dead monitor for one good reason. If it had a working one the seller could pop in ANY Jamma board and sell the game for $200-250 EASY, or pop in the correct one and get $400. And anyone who would own a game that didn't have a board in it would know this.