The trip to Trenton NJ proved to be very fruitful. The 16GP4 tested very good.
Filament voltage set at 6.3 volts
Cutoff as good as I've seen in any vintage tube in a while.
Emissions with cutoff not zeroed
Emissions with cutoff zeroed
I really can't expect much better than that. Thanks to everyone for your help and a special thanks to Bryan for his generosity and Kevin for his efforts in helping me find this and kicking me in the butt to go get it!!!