Ed, Ray;I worked on a friends ICOM R-71 a few weeks ago. It has a built-in 70 Mhz IF port that is buffered. It's fairly easy to find the service manual online to get the technical details on the port.
I had a few minutes to play, so I attached a Nano TinySA to it. That worked, but I thought a couple issues would limit it's usage. First, the port only output the bandwidth of the first set of filters. I was hoping to see the full 30Mhz up-converted to 70Mhz. That means you must know the tuned frequency on the radio and do some math to translate the spectrum view.
To complicate it a little more, on that radio at least, the output of the port is inverted frequency wise. IE a signal higher than the tuned frequency shows on TinySA below the tuned "Center Frequency".
My conclusion was the port provided little value. To build something to use it would be so involved, it would be simpler/easier to just get an SDR like an SDRPlay.
Just my thinking to what I saw with no monetary gain or lost.
Mike N8OOU 73