One could do that, but it isn't preserving the 8754A as it was originally intended to be used, it is making a hybrid VNA with the automatic switching of a 8753 etc. When we bought 8754A in the 1980s, it was the cat's meow for doing measurements up to 1 GHz. We stocked up on good directional couplers, like the Narda 3020A, and did whatever test we needed with a single path setup. I was designing high power cavity amplifiers for FM broadcast transmitters at the time, so it was great for sweeping the big circuit for resonances and gain. People designing antennas had them strapped on their range to sweep the antenna with a solid state power amplifier to boost the level. Using external directional couplers, that was very easy to do using the 8754A. I even saw one up on a tower, as heavy as they were.
Then came the Hp3577A. It had calibration built in, that could be run to normalize the setup. We bought that for the transmitter work, only ran to 200 MHz though. I moved on to another company, where we had a Hp8409A VNA, which was a Hp8410C network analyzer, test set, switches, Hp8620 sweeper, and a 9836C computer. It was two racks of equipment. Clunk clunk clunk. The Hp8510A came out and revolutionized measurements, all in a single rack on wheels. I donated our 8409 to a university. Quickly after 8510A, the Hp8753A revolutionized the world again, and they were hot items! I moved to another employer and by now I have operated every network analyzer until the latest models from Keysight, and I just got one of them at work, getting used to it. The only one i never laid hands on was the 8753D and some of the PNA models after the 8753 was out of production.
If it were me, and it isn't, I would not put a lot of work into trying to make a 8754A do things that weren't intended, when you can find a lot of amazing network analyzer capability either used or new from so many sources. People are making measurements with a hundred dollar devices now, although they are no where as good as a real bench VNA. I do recommend that you pick up a couple of Narda 3020A broadband directional couplers, or the HP equivalents, to make good use of the 8754A for insertion loss, gain, reflection, all done by hand. It will make you understand the measurements very well using that box!
Sadly, an old engineer at work bought a 8754A back in end of the 1980s, when it was about to be discontinued. They didn't have the foresight to spend on the 8753 at the time. That 8754A sat in a cabinet, hardly ever used. I ran across it about 5 years ago, with the original manual. As much as I hated to do it, I sent it to our surplus/salvage group and hopefully someone out there got a unit in perfect condition after it was auctioned off at Bentley's in Albuquerque. I strapped the manual to it with tape as our salvage/surplus operations tends to throw out all the paper and cables. Cool old box for sure. Probably fun to repair too, so much RF and analog in it.
John Lyles
Jinxie