Looks awesome, isn't the 120 a beast
Might be worth trying to piggy back the 80 on the 120. The rings on the bigger scope should have a series of threads - on my 100, there are 5 iirc. A mate of mine with greater skills than I (and the tools) cut an aluminium plate to straddle between the rings and secured on the top with a screw at each corner. On that plate you could then mount a dovetail clamp to hold the 80. Having the clamp is useful as you can quickly and easily remove the smaller scope.
Depending on what you're going to image, you could use the other scope as the guide scope
