Those 74XX/74XXX seem to be 74AC, which if I remember are high speed CMOS. These were susceptible to blowing out when the amperage got too high. And from the looks of it, most seem to be part of the floppy drive circuit or the area there off. A bad or "killer" external drive was attached to it? It one those IIGS 3.5 uni-drives put in?'

At least you got it back running again. That's great!