In a discussion on 2012-01-20 in the New Studer list, Todor Dimitrov posted the differences between the record and repro boards between a 1/4-inch and a 1/2-inch two-track A80RC repro cards. Here are the changed components for the 1/2-inch version. There are five different oscillator versions in the manual, including one for 1/2-inch.
RECORD: C34=68pF REPRO: R1=100K; R21=330
Note that the mechanical modifications between 1/4 and 1/2-inch tape handling may be substantially more complex in terms of tuning the transport. I know of no definitive notes on this subject. [Added 2013-10-09]
CBC A80RC Repro capacitor mod
I had previously posted in the original (and now reconstituted) Studer List on 2008-04-24 that there were other extant and possible modifications. Here is a slightly edited and reformatted version of that post: