Sounds like you wisely did it carefully.
Generally, when fitting is required, it's not the slide that must be adjusted, but the lug area under the barrel, which sometimes doesn't fit in various versions of the 75B. Your's is the first case I've read (or heard) about where that was a problem. Is your kit, by chance, one of the newer Kadet KIT II models?
Happily, the beauty of the Kadet Kit design is that fitting doesn't seem to be critical -- just getting it on the frame is the most important part.
That's because the upper unit (which is the barrel, the housing (that looks like a slide, but isn't), and the sights) is a single unit, and there's little or no chance of "play" or movement, even if fitting is a bit on the loose side. The only part that moves -- the rear of the unit -- doesn't have any effect on barrel/sight alignment -- because those pieces are, in effect, locked together. If you use the sights, you should have an accurate unit.
I suspect you'll be very pleased with the accuracy. I sold a Ruger MKII Target Competition (stainless, with the longer, slabsided barrel), because my Kadet Kit was just as accurate. The 75B (and now 85 Combat) grip just fit me better than the Ruger. I still have another Ruger MKII, though.
