Dr. Gorsky's question came up a day or so ago from Mr. Steele, about how to identify if a single arm would accept the trimmer installation. Curtis' answer was technically correct, but I don't see it as required equipment for Dr. Gorsky's serial number aircraft.
TCDS 3A15, item 603, is the ATC-35 aileron trimmer, Item 603 is not listed as required equipment for either Dr. Gorsky's or Mr. Steele's aircraft.
The ATC-35 trimmer is in the V35 IPC as an ATC-35-107 applicable to D8336 & after, 35-380072-1 is listed in the 33 IPC for S/N CD1062 & after.
Textron's parts website supersedes the ATC-35 with the ATC-35-107, then to the 35-380072-1.
These are optional equipment items. The answer to Dr. Gorsky's question "Is it possible to add trim adjustment to my throw over yoke or must I find another yoke? If so, where might I find one?" would be the same answer I gave Mr. Steele, basically if there is a center hole with three 8-32 tapped holes symmetrically around it, it likely would accept the trimmer. Textron is showing stock on the 35-380072-1, at a list price of $2800.00+. The used market may also have them.