I have what appears to be a common issue, a very leaky petcock on my '96 VFR 750 RC36 ii. The petcock is no longer available but the one on the NC30 looks very similar from the diagrams, has anyone tried to see if one might fit? There is a spicot on the side, maybe this is a vacuum petcock in which case it won't work?
No idea if the configuration is correct, but you can certainly pull vacuum from one the synch ports on the head next to the intakes. That is likely where the NC is getting it from. Also very easy to defeat the vacuum operation on most Honda valves. Honda is notorious for making something that could easily be identical dimension wise, looks exactly the same, but making it slightly different and not suitable.
NC30 and NC35 use vacuum if I recall correctly. As long as the mounts are the same you should be good to go. You could also rework the vacuum system which is what I am working on tomorrow for the VTR.