Sounds like you shorted 50 volts to the switch matrix and blew your U20 switch matrix chip on the CPU. A blown U20 can cause F115 to blow, which is most likely why the fuse continues to blow. Sometimes U14 will be damaged too, so keep that in mind if replacing U20 doesn't fully cure the problem. Be sure to put a chip socket in for U20. Your exact scenario was common enough that later CPU board versions came with that chip already socketed. Also why later games have an interlock switch to cut the 50 volts when the coin door is open.

To answer your question on the LM339, yes both 339A and 339N will work. Replacing U20 will likely take care of the fuse blowing and fix all your woes. It's the one that took the hit when the short occurred. Suggest you replace U20 first and not do them all just to do it. Beyond U20, U14 can also take damage in this short scenario, though not always. So before you mess with the LM339 row chips, I'd look at U20 first, then check U14 if there are still switch issues.