My plans show 9 revisions, R1 is dated 11/83 and reads "Altered Stab Attach" with callouts to the angle bracket. The callout shows up on the left side of your photo here:
http://s74.photobucket.com/user/Aman...9f1a9.jpg.html
Also worth noting is that R6 (9/93) reads "Added F-419 & Note" and it looks like you've got a 419 underneath - I'm not sure whether there was something there before or if you've got a mix of revisions. I don't think rebuilding it to plans would mean major changes back there but it's a tight space to work in. Finding pre-'83 plans to check the install might be difficult.
Definitely worth a call to the factory.