Thanks for that, although testing like that is a little outside of my skillset...
If you have a VOM (or a disassembled flashlight, some tape, and a few bits of wire) you can probe the cable/sense lines and see if they match up the way they're supposed to; that's certainly a lot safer than poking around inside a monitor with the top off.
I still don't have a video card with dual outputs, but is that a better solution than using 2 video cards anyway?
Personally I'd recommend using two video cards with native Apple DE-15 plugs. I strongly suspect you're going to have issues trying to use these old monitors through VGA adaptors. (I don't know of any dual-monitor cards that have DE-15 plugs and will work properly with monitors like the Portrait that use the oldskool sense-line arrangement without some substantial fiddling, but I don't know a lot about PCI Macs of that era. The only OS 9-compatible dual-head cards I know of are a few GeForce and ATI Radeon Mac Edition cards that have VGA and DVI ports.)
