Adding 100Mbps ETH to an R&S ZVx Network Analyzer

[sixtimesseven]

I would really like to add 10 or better 100mbps ETH to my Rohde Schwarz ZVR VNA.
There is a R&S option for it, however it's only base10, not available used and likely obsolete and or too expensive so 

The instrument runs Win NT 4 which I have zero expirience with so far. On the bright side, the backplane / mainboard / plugins do have 3x ISA extension slots so should be straight forward(ish).

At the moment I would be interested in pictures of ZVx's with installed ETH options as a reference 

[george.r]

What a delightfully weird piece of gear. Seems like it runs on an Eurocard SBC. WinNT4 looks like a crossbreed between W98 and W2k (because that's what it essentially is - a W9x-ish interface tacked atop an NT kernel, Windows 2000 being NT5). You won't find too much difficulty fiddling with it. NT4 lacks a device manager, but that's the only major weirdness (or so have I found). Something like a 3Com 3C515TX ought to work. The Ethernet card R&S originally installed is an SMC 8416 EtherEZ. But anything with the proper NT4 drivers should work.