You get the test pattern on the screen so I believe you've got that little box with adjusts for brightness, contrast etc. for your Barco. If not, no problem, there are just a few standard pots and switches inside there and it's easy to build yourself. Look at the service manuals for schematics.
The test pattern itself is just a RGB signal fed into the barco internally, so your Barco seems to work just fine. But there is one clue you need to know: All of them have two "VIDEO" bnc connectors, but in standard 600 and 400 models these have no function - you might have one of the many "RGB-only"-models. So try to feed a RGB signal into the Barco. Remember that he needs RGB-S (composite sync, negative polarity) on only _one_ sync connector, thus called "composite sync". Search for epanorama on google for schematics if you don't know how to get an composite sync with negative polarity from your VGA connector, i am not allowed to post a link in here yet :-(.
Hope that helps, otherwise you can contact me.
P.s: Sorry, I believe I didn't read your message carefully enough. The first thing to to is to connect the RCVDS using the 15pin connector on the barco and the RCVDS. As fas as i know, this cable is internally connected 1:1, so pin1 on pin1 and so on. Then you should be able to get the test grid by activating the switch on the convergence board with all tubes G2 switches turned on. If that works, you can connect the RGB-S inputs of your Barco either with your RCVDS and use the RCVDS inputs or directly connect an RGB-S signal into the barco. You find the schematics to connect an VGA signal from your PC to your barco on the website mentioned above. It's in the category "Circuits - Computer".