I haven't had access yet, but I have the complete setup. I hoped to be able to use the existing base plate. If not I will have to rethink everything.
If it was a DIRECTV HD setup with their behemoth "Slimline" dish, it won't work. The Slimline foot plate (and that of its predecessor, the AT-9) won't "hug" the smaller mast so it would require a some manner of bushing (or perhaps a sleeve welded on to a DISH tube) to provide the rigidity and holding power necessary to withstand a good wind load.
I would imagine that adding flat spacers will simply cause the through-bolt to flex where the flat spacer meets with the round tube.
One outfit sells a clamp-on adapter but it looks pretty hokey with a couple of setscrews threaded into a split tube.
On the other hand, if it wasn't an HD dish, the 1000.2 should slip right on.
Come to think of it, if it was a worldDIRECT dish, those came with a 1-3/4" mast.