"I've read on here that the carbs on this model (PD42B) aren't everyones favourites and they are different to the earlier models - Was planning on getting Keyster Carb Kit [Keihin PD42] from
https://nrp-carbs.co.uk/shop/index.php?route=product/product&product_id=450&search=pd42 but was sure if they would definitely fit mine as they say CB750F4 and also PD42 but mine say PD42B. Would these work or would there be better and cheaper options out there?"
PD42 is the type with "B" the specification for engine as example. F3 was USA runout model for the F2 in UK terms and uses different jet sizing to the K model you have. So they fit but aren't to std flow volume as original. You'll specifically need K 7 or 8 to be correct, I can get exact details for jet size for you if needed when I get to look it up in manual.
I like the PD carbs (can see the reservation in working on them in being fiddly) but they are a very well designed, accurate and more advanced carb set than earlier models.
Running strategy is to have the fuel metering more accurate for constant running with supplimentary fuelling for acceleration via pumped additionally as you twist the throttle open. Without the pump operating correctly you'll not be accelerating much
so verify that's healthy too. Be hyper diligent in cleaning all fuel/air passages else you'll be dismantling again.
They genuinely run really well if in good order and give particularly good control/response.