Rossco,
Do you HAVE the Robart tail wheel for the GS P-51? If you do, it will be much easier to visualize the installation .
You'll need the big gear assembly with the single leg for the GS P-51 and the small plastic gear assembly for the 40 size plane.
For the GS you will need a hole 6 5/16" long, 1 3/4" wide at the front and 1 11/16" wide at the rear of the hole for the gear to go through when in operation. The front of this hole "opening" is 1 7/16" back from the rear mounting hole for the radiator scoop.
The easy way is to cut two 1/2" square lengths of hard wood to fit inside the fuse and after you have these two "mounts" pre-fitted you can then mount them to the tail wheel and install as an assembly.
I did this with the push-rod and steering cables already attached TO the tail wheel.
Go to the www.robart.com to see what you need and if you use a air operated tail wheel the installation will me easier still.
Sorry, no pics, everything is packed away for my move to Nevada.
Chuck