While I can't speak much to the designer of these head gaskets, I don't like to put them in with coolant passages that small. Every block I've taken apart has had mountains of rusty sludge on either side of those sad little 1/8" holes. I have had no overheating problems after expanding the coolant passages to 3/8". I recommend the Fel-Pro gaskets because they'll seal a rough deck like yours better than anything else. They're also one-piece, and I don't like the idea of drilling MLS gaskets.
As for the boogers in there... Looks to me like what ethylene glycol does in an overheated motor. I have a habit of rednecking old trucks back together, so I assume you're not going to pull the block. If you brush the holes out with a pipe cleaner & bolt it back together, flush with the garden hose (don't let that goop get in your radiator, and check that sucker! It could be the cause of your overheating) before adding coolant and you should be good to go.
I agree, it looks like the middle two were run a little lean, but the gasket being blown will skew any visual results. I wouldn't worry about it, just read the plugs after it's all built.
The 2150 is a great carb candidate for this motor. I have one feeding a D-port head on my truck: 1.08 venturi, 4.5 power valve, #56 jets, and a manual choke. It runs a bit rich at 2500 feet elevation so I could probably back mine down to a #55. If you care more about mileage than power, order a 5200 for a '74 spec Pinto 2.3 on RockAuto. Less emissions hardware & they're already set up for 108HP.
Speaking of power. Older 2.3s should always get stem seals whenever the head is off. While you're in there... Head to your local JY & get yourself a Ranger roller cam, '89-94 years, and get the roller followers. Bolt-on upgrade for $30 or so. No more wearing out flat tappet cams, plus a little more power
