Yeah, I think that was the case.
I uploaded a couple of videos on below thread,showing the operation of this Nikki carby primary and secondary valve operation.
http://www.nissanpatrol.com.au/forum...l=1#post706761
RB30 & TB42 Nikki carbies are essentially the same.
They are either tuned differently or jetted slightly differently to suit each engine.
The replacement Nikki carby for sale on ebay is listed as suitable for both engines.
A good indication that it's the same carby external and internally.