If it's that bad, just get another shifter body.
I think the Muncie shifter is the same. I once bought a $10 swap meet shifter, no idea what it came off of, but it was a perfect match to the '65 GS shifter.
There are repo bodies available. Here's one from Lutty's:
http://www.luttyschevy.com/i-20831814-linkage-assembly-shift-gate.htmlTo repair yours, you could either weld up the hole in the body and resize it, or drill it oversize and install a bushing.
If the plates are also worn, you're getting into a lot of repair time.
Here's a pic of mine, disassembled and blasted.
The body is two pieces welded together, the weld must be cut to disassemble it completely.