Jizzo,
I tried doing the same thing recently and gave it up. Maybe your luck will be better (and that old satellite mount will be in the best place on your roof for reception - I'd follow Diogenes advice and walk around up there with the 4228 when you get it to see if another spot is better), but there are two things to consider:
1) the sat. mount is probably 1.66" diam. and your 4228 hardware won't fit a mast thicker than the standard 1.25" - a plumbing-type fixture might fit the transition in diameters possible in a solid enough fashion, or maybe not.
2) I could never get mine to stand up quite vertical (no jokes, pls) in the direction it already pointed, or by taking out the hardware and reversing it in its foot. It was always a bit out of plumb, and looking at a 4228 on a 5' mast just resting in the too-wide sat. mount mast, I just couldn't stomach the sloppy (and downward-sloping) aspect.
Went to a completely separate mount at the other end of the house, although the old sat. one, with its footing already installed and waterproofed, WAS tempting. Maybe it will work out better for your situation, but I'd take a close look at it and fiddle some before counting on it.
