Shift Coupler

[Oldman]

Looking back at your original pic. of the shift coupling, the bushes look like a poor fit .....ie. the steel casing has the gap/play between the bush and the case.
Compare it to the Rhino unit....there is no gap between case and bush.....
No bolt modification is going to rectify that, in my opinion.
My understanding of the way the coupler works is that the bushes ease the mechanical shock between shift rod and selector shaft. If the connection was over tightened it would prevent the bushes doing what they were designed to do....absorb shock.
I think your solution of new /replacement bushes is the answer 
Me ?....I'd probably spring for a new Rhino unit....buy once, cry once as the saying goes.

Even the JK option looks better than what you have.....I'd ditch the metal tube, ( it's there to re-use the stock, 2 coarse threaded screws), and replace it with a H/T bolt & nyloc....
https://www.justkampers.com.au/311-798-2...2-bay.html

Or there's this one from Victoria ... different bushing system and Australian made:

https://www.vwperformance.com.au/product...um-1968-on