Jerry,
You may be trying to accomplish something that is not necessary. What is the position of the arms on the side cover of the transmission? If both are pointed down you could obtain another shift rod similar to the 1-R shift rod for 2-3 and install it in the same manner as on the TF/60's trucks. It will probably take some bending for it to fit.
If you have the side cover that has the 1-R shift arm pointing down and the 2-3 arm pointing up, it is probably a car transmission which has a similar set up like your stock AD configuration.
If this is the case you could get the truck side cover and install it like I mentioned above.
I just did a 6 to V-8 conversion on a 55 and used this procedure.
I hope this helps, Fred

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine