I know that they're not liked because of physically cleaning them, but they are good carbs that run jetting closer to ideal with enrichment supplement only when needed, as opposed to essentially running rich all the time for "ordinary" carbs.
I thought the a versus b spec was to use slides with different cutouts to give the different identification.
For the PD42 (750 F2 and 750 K7 are paired in Honda workshop manual) the A version is listed for the F2 with B for the K7 with subsequently 105 and 110 main jets.
These are in the specification pages with the 750F in a left column accompanying the 750K in right column for all specs. But interestingly in the carburettor section they've swapped the headers, typo? which then swaps the a and b spec over! So even they seem confused
The K motor is orientated toward lower revs and torque peak so could explain if the slides were different to trim response at more typically used rpm for that bike versus the F2 With lower gearing and raised red line.
I've not seen them for years next to each other, so it may be worth you comparing the throttle slides to see if they differ if you've both types in front of you.
