The NB idle control valve is electronic only, the NA Idle control valve is electronic and also contains a Wax bleed valve. The NB valve has access to air pre throttle plate so it doesn't need a seperate air feed. if you look inside an NB TB you'll see a hole infront and behind the throttle plate, this is where the ICV can access and output air respectively

Physically the NA ICV is much larger so you can't simply bolt one onto the other. Although the actual TB mounting is identical, so you could convert to an NB TB and delete the wax valve in the process.

 

Thank you Mr Slow, you have been extremely helpful.

I think I'll try to source a NB throttle body for my NB6 intake manifold. Just a pity they're so expensive on ebay!