Found this 1960 truck shop manual online a couple of weeks ago. Covers 235/261
engine specs and overhaul. Shows different specs and method for checking 235 and 261 timing.

No mention of different timing gears in manual (p. 8-25 and 8-26) Might be something useful for you if you don't already have a manual like this.

http://www.canadianmilitarypattern.com/1960%20235-261%20Engine%20Manual.htm


"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson