Good Evening, George
I have the same Chromega drums and have located a Chromega instruction sheet. Officially, "the 8 x 10 Color Print Processor requires two ounces of chemistry (sic) for conventional papers and three ounces for resin coated papers." The 16 x 20 drum "requires eight ounces of chemistry (sic) for conventional or resin coated papers."
For what it's worth, however, keep in mind that these instructions were written with expensive color chemicals (NOT "chemistry"--sorry, can't lose the old English teacher habits) in mind. I use the 8 x 10 drum for film processing, occasionally for a quick B & W contact sheet or two, and almost never for prints; the 16 x 20 does come in handy for prints since it takes a lot less room than a set of large trays does. When I process film, I like to have at least eight ounces in the 8 x 10 drum, often ten or twelve ounces. I haven't printed any 16 x 20's for a while, but I'd probably want twenty-five to thirty ounces in the large drum.
By the way, Chromega's recommendation for an 11 x 14 drum is five ounces for either type of paper. Hope this is useful.