modifying stock AOD shifter??

Have you thought about using an aftermarket one?

http://www.partshp.com/Shifters.htm

Look at the Hammer shifter

I have this shifter, but not on my Mustang.
It is actually going into a Samurai (Don't ask).
But it has a ratchet mechanism, that let's you "hit" it for each gear...
In other words, it doesn't have a button you push in and then go from 1st to O/D...
You actually have to go from first to Drive, and then hit it again to go to O/D...
You can also go from 1st to D, and then smack it back to 1st to hold second too, although I'm not sure how well that feature works, since you have to be quick about it?

Unless your just looking to do it yourself, why dont you save yourself the frustration and go with the B&M shift gate

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=4281&prmenbr=361

Part #130 80788

You drill out the rivits holding your stock shift gate and rivit or bolt in the B&M.

You can shift all the way down to 1. When you shift up, it will only go to D then to get to OD you slightly depress the button and it will shift up to OD. The rest of the shift features are stock. I have one in my 91 and it works great and for 25.00 its a good deal.

what your showing would probably work. maybe you shoud go to your shop and have them do it, incase they run into any problems?