IF , as suggested in another post, NC21/24 and 30 carbs are VERY similar , does that mean NC30 jet kits would work in a 24 ?

Technically yes, but the needles are significantly different, and the main jet sizes are different.

If all you want is bigger main jets then you can just order the jet through a workshop.

You didn't specify sizes of the jets in the kit, Don't think so tho.

NC21/24:

Pilot Jet: 35
Main Jets:-

Front: 112
Rear: 110

NC30:

Pilot Jet: 35
Main Jets:-

Front: 122
Rear: 120

Don't suppose anyone has any 112's kicking about they don't need
I have 115's on the front for some reason. Want to try either uppint the back to 112 or putting front back to standard.