The parts Jenne and I ordered arrived today, so we made a long cable for Guralp 1 using a 24 + 1 wire 70 meter long cable, a female 37-pin DSub, and a 26-pin milspec. The pin map is the same as the one I specified in my previous E-log. I soldered both the milspec attachment and the DSub attachment, and used a Multimeter to check the connectivity of the cables. 20 of 20 connections worked (beeped), so I plugged the cable into the Gurlap 1 seismometer and the Guralp box.
The time series comparison for the two cables
New cable: (I had to move GUR 1, so it's still stabilizing in the X and Y time series)
The current signal spectrum
The BLRMS on the seismic strip also look similar using the two cables - it's more visible on the wall, but I will include a StripTool picture:
New Cable BLRMS (similar to old cable BLRMS)