After deviating from Bill's design I have come back to the fold and built the mixer as he described. Another insight is that I've come around to putting each functional stage on a board of its own rather than trying to build the whole project on one board. I don't have a 1k:8ohm audio transformer so I used a powered speaker purchased at the MRARC auction last week and that seems to hum for some reason when connected (I tried battery power on the radio).
My VFO drifts wildly but with care it can be made to work. Here's a bit of reception from 40m this morning.
Next I connected VK3HN's VFO up and see how that sounds.
Rock stable as expected but I get clicks as I tune.