Wonder if you use the aftermarket 'T' handle with your old button, the notch may be worn smooth for that 'light touch' feel.

Other than that, I don't know.

I have had a handle off a turbo 350 and a handle off a turbo 400 they both looked the same to me, but I did not look that close either.

As far as I know there are different mechanisms under the console depending on which gearbox you have. One is linkages (350) and cable for the (400).