🚀 go-pugleaf

I've recently been give a Philips 19in RGB monitor which originally came
with a dedicated card for a PC system running AutoCAD. I'd like to get this
working on my PowerMac 7100, but I have an apparent incompatibility between
the video output of the Mac and the input to the monitor. 

The basic problem is that the monitor has only three BNC inputs (R, G and
B) and does not have a separate sync input. From what information I have
been able to glean in a web search, the monitor uses a combined sync on the
green input (I hope that makes sense - the relevant message was in German
which I don't speak!).

I've also been given a Supermac Nubus video card and cable, which has the
standard Mac DB15 connector on the card and a lead from the DB15 to four
BNC connectors. However without the sync. input, the 'picture' on the
screen is a meaningless jumble. 

Is the solution to this problem simply the creation of the correct adapter
cable (in which case, what is the configuration - I'm handy with a
soldering iron and I object to paying over the odds for cables I can make
myself) or do I actually need to invest in some more hardware and if so,
what am I looing for and where is the best place to get it?

Help would (obviously) be appreciated.