UPDATE:
I have figured out a way to accomplish this with the 2 mounts and the 8" adapter, but have no idea how it will work long term.
Once you put the 8" adapter in, you have the smaller mounting pole size.
However, for lack of the proper terminology, it is a male and so is the J adapter of the mast. All the dishes have a "female" with bolts to tighten down - so I have no idea how one would use the 8" adapter with 2 males as it is sold.
Anyway, you mount the smaller 8" adapter to the SC .75m so you have the smaller male on the bottom side.
After spending the day running around to Home Depot, machine shops, electrical supply places and plumbers, I finally found that you can use a plumbing dresser compression fitting. Home Depot/Lowes does not have one in the size needed, fwiw. You need to find a real plumber or plumbing supply.
The inside of the compression fitting appears to be 1.75 inches, though i would take the 8" piece in with you to test it as some brands were tighter than others.
By using the dresser on the J of the mast and the 8" adapter attached to the SC Dish, it works.
God knows what will happen in heavy wind, but we will find out.
FWIW, its like this - though I am not saying this one is the right one for ordering over the net:
http://www.standardplumbing.com/catalog.html?wscdet_show=000000000105055035#top