Spindle-To-Pivot Distance

You asked whether I have experienced this. The answer is yes. About 25 years ago I once fitted a Rega arm to a Project turntable in place of the Project arm. The effective lengths of the arms were different by a similar margin.
I didn't know much about tonearm geometry then and I wanted to see if it would be an improvement. It wasn't. The result was exactly as I described - mistracking and distortion.

So I can tell you from both a theoretical perspective and from experience that it is a bad idea.

If someone actually did this and heard it sound that bad then there you go.

Sounds like you could do it right and only have to put up with it looking bad. If that is the case looking bad is better than sounding bad.

Make a mounting plate that will hang over the edge of the plinth. Wood will do fine! Or use acrylic! A rectangular piece with a mounting hole.

Install a slidable arm base, slide to 250mm to play a record, slide to 240mm for good looking.

https://i.ebayimg.com/images/g/hz4AAOSwuhheVlOd/s-l1600.jpg