[Amps] 2M W6PO Amp Cavity Zo calculations

[Charlie]

Putting some parts together for a 2M amp. Like the W6PO design. Antennaworks
has a nice write up of the design choices in their manual online:
http://antennaworks.com/

I have 2 questions. 
1) On page 21 of the manual, it states that the Zo of the resonator is
"approximately 130 ohms". I don't have the referenced ARRL Handbook, but my
calculations come up with about 70 ohms. I have used 2 formulas,  Zo=138
log(R2/R1), and Zo=60 ln(R2/R1). What am I missing?
2) The bottom of all these W6PO designs have excess lengths of pipe
extending beyond the short. Notwithstanding the need for some excess to
allow tuning, is there any reason to not shorten the pipes and the excess
cavity? Maybe shorten the height to about 8 inches?

Thanks for the input,

Charlie N6CFH