Adjust fore and aft on old Corbin backrest

[JohnUSA]

New to me 1993 Aspencade, with a Corbin of unknown age. I was trying to sort out how to adjust the fore and aft position, as it was too far back for me when I rode the bike home.

Remove seat and flip it over, and here is first look. You have to loosen the locknut and slide the bolt to set the backrest position. I discovered it was already as far forward as possible.
In order to gain more forward position, I needed to extend the slot. Drilled a hole, and then continued on with a Dremel.

Here is first pass with the Dremel:

All dressed up and ready to put the washer back on, take it for a test ride.