If you want to work on the Tektronix 7S12 TDR/Sampler plug-in, you can use two standard 7000 series flexible extenders (or similar) to operate the plug-in outside the mainframe, but even when you've done that, it is still hard to work on. The bulk of the electronics in this plug-in is in the form of two daughter boards which plug into edge connectors in a mother board, and you can't get at these at all readily.
Tektronix used to sell an "extender board" with part number 018-0064-00. This allowed you to elevate one or other of the boards out of the plugin. I have never seen one of these boards for sale, or even seen a photograph of one on someone's web site.
As I wanted one I designed a PCB layout for a double sided extender board, and the Gerber files are available for download here: 7S12 Extender Gerber files, and here's a photograph of the completed board.
I'm sorry but I don't have any of the dual readout 0.15" pitch 36/72 way edge connectors with extender card bend available, and the supplier from whom I bought the one you can see in the picture doesn't have any left in stock.