Here is an ad which I believe was first used in January 1971 in Audio magazine.
If so, I would find this interesting since it has the Seattle, WA address (in the Richmond Beach neighborhood of what is now Shoreline, WA).
Considering that there is a several month lead time in advance of an issue coming out, the amp was either a bridge amp, a Kelly DeYong amp or an empty chassis at the time. The PL0171 pc board was not used until sometime after January 1971.
By the way, the Seattle address no longer exists. I believe they were using the bottom floor or basement of an old grocery store (at the address noted in the ad) which predates their move to the bottom of the grocery story at 405 Howell Way in Edmonds, WA. If my memory serves me correct, Steve Johnston, Greg Johnston and another friend (whose name escapes me) were living down the street (from this location) at what was once the Handy Spot Market. Bob was living near "Firdale Village" a couple miles away.
NOTE: Credit must go to the phaselinearhistory website for this photo.