Modifying a t grip auto

What car / autobox ?
Every auto I'd have the gear selector has been connected to the gearbox with either rods or a cable so no problem changing to a different type as long as you are prepared to adapt connection / mount.
One car had a Ford C3 gearbox with a US B&M Quick Shift ratchet change that was cable operated which replaced the original Ford T handle type.

if you have some money to throw at it, a Lokar shifter would be a way forward for you. they are not cheep , but they are well finished and look sweet. I have recently fitted one to a TH350 gearbox and the quality is very good. Like most things though, there would be some degree of improvisation for your adaptation though.

I used a soarer auto box knob on a supra. Had to shorten the shaft slightly other than that it fitted right on. Looks the part too.