Hi Colin,

> I am about to try an NE602 mixer circuit.

That chip is not worth wasting any time on. There are
much better, yet simple, alternatives that can handle
huge signals without problems. Example:

  http://www.xs4all.nl/~martein/pa3ake/hmode/index.html

With suitable transformers, these chips will work UFB on LF/MF.
Considering the high level capabilities of these mixers, make
sure that you wear adequate eye protection (welding goggles)
before starting Argo :-)

73
Johan SM6LKM