Are there any estimates or hard figures for production % and totals for '65 interior trim codes, and manual transmission vs. automatic?
There is no single source (like a Marti Report) for Fords built prior to 1967. Thru the efforts of Jim Smart and Jim Haskell there is the Mustang Production Guide, Vol 1, that does have a statistical analysis section on "their" data, plus some bits and pieces of Ford Marketing numbers, such as "Mustang Does It". All the figures are "close" (or not depending on you approach). What you will not get is a basis for any claim of "1 of" for any early Mustang.
Jim