I ordered a delrin shift knob (TS-UNI-108a) and a subie reverse lockout collar (TS-UNI-027) from Torque Solutions. The collar turned out to be a little too tall, so I shortened it 3/8". Here are some photos of what the reverse lock out looks like with the shift extension rod and the lockout collar in place.
The lockout collar after shortening and repainting.
Installed.
close up of collar and reverse lockout mechanism.
I think this finishes off this area better than the flat washer I was using. Now you don't see the spring anymore.