Brian, Do you have a schematic for the power supply you used for the T-368 exciter? I have one here and need to build a supply. Thanks. I don't think anybody mentioned it here but most of the PTO's of that type have a fundamental frequency of 1-2 MHz so you can cover 160 by bypassing the doubler.
The T-368 PTO has a fundamental frequency of 1.5-3.0 mHz. The lowest frequency range feeds the PTO signal directly to the output stage. The other ranges insert one or more multiplier stages in between.
Another mod I made to mine was to add a vernier drive mechanism to the main tuning knob to slow down the tuning range. I used a Jackson Bros. mechanism. They come in two forms, to English measurements and to metric. The English size fits the shaft snugly with zero slop.