yeah theres some good info at that site but.... he`s completely off the mark with the stuff he`s written about the Yamaha Dynamic #40. I own 3, they were not export models so the info I have comes from Japanese guys who own some, and the Japan Vintage series of books I have with extensive articles on the Dynamics. They were not cheap copies of anything, they were Yamaha designs and the bracing was patented by the man who designed it. They are not plywood as he states but all solid wood...the S series Dynamics, the S-50 and S-70 were plywood...and came between the Dynamics and the light green label FGs that were introduced mid `60s. When the Dynamics #40 was first listed in 1961 it retailed for $65.oo, a time when the average Japanese office worker made $100.oo...a month! I know because I teach some retired folks here who told me, one of my guys said his starting salary was $84.oo a month. 
I sent a mail to Frets but never heard anything back, I`m pretty sure I linked him up to the site I visit when I have questions about the Dynamic line...theres a small, but growing, nearly fanatical following of the old Yamahas here, I mean pre FG models, which every one seems to be after these days...me...I`ll stick to the all solid wood Dynamics, I pass by red label FGs here every day.
Heres the on line museum...a start for your old acoustic guitar blog...
http://www.geocities.jp/mmasmcb/catalog.html
and heres a link to somebody playing a few of the Dynamic models...there were quite a few...
http://www.geocities.jp/mmasmcb/kyoku/original.html