Here you can see a size comparison from the front of the 2 CYB monitors (the 17 and 21).
With regards to your Conrac tuner offer, I'm interested, though I don't strictly need a second one. If you look at the above pic you'll see my Conrac tuner, which has illuminated channel numbers. I wouldn't mind a second one (especially since yours is slightly different), but if you think you have use for 2 I wouldn't want to inconvenience you.