Many thanks to all who replied, both here and by email.
They sound like a great tube for LOTS of purposes. My
favorite suggestion was building a regen, using each
half in place of the 6AQ5's called for in the ARRL handbook
design from the 50's!

How about an oscillator / amplifier for HF, running low
plate voltage for a relatively low RF output? Seems they
should be able to do that - and having a separate oscillator
stage it wouldn't be prone to runaway and exessive crystal
current. And it would look VERY cool!

What sort of plate caps were used? There are just pins, and
it looks almost as if there would have been a ceramic gizmo
like a tube socket to have bridged the two of them....

Again, thanks for the info!!

Dave