Yeah Nigel, your supposed to match them, but really not necessary.
How did I know the suppression? Estimated for now. Read voltage peak to peak levels. Seen it enough times.
"Full quiet" is 60 db down. It might be kind of a slang radio term. But it is still used fairly often like in PLL when talking about the level of the first phase sidebands. They should be atleast 60 db down.
Yes an attenuator can add to suppression. After the mixer (post mixer) the signal is created with two signals, by attenuating unwanted components from one, it is possible to eliminate them from the composite result.
Yeah that is allot of suppression. That's a good circuit. Thought I would share that with you. I've used them before.