I may not qualify as a "nice person" but I'm happy to help.
With the tape measure hard against the front edge of the seat cross-member (top of the photo below) the hole starts at 40mm and ends at 160mm.
Attachment:
Remote Gearshift Hole 3.jpg
From the middle of the downwards curve on the right side of the old starter button flange to the right edge of the hole is 80mm.
Attachment:
Remote Gearshift Hole 5.jpg
The hole is 110mm wide measured along the curved tunnel, not straight across the opening.
Attachment:
Remote Gearshift Hole 4.jpg
The corners are smoothly rounded.
Give that a try. Let me know if you need more.