Spindle-To-Pivot Distance

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

If you are looking  for a answer to your question  you probably  came to the wrong forum.   Some engineers  way  back in time came up with the two null point system and the various percentage of distortion  from there.  There  seems to be 2 to 3  popular  null point systems.  So if  you go by there  methods you have 2 null point with everything  is supposedly  perfect and the rest  goes into various  degrees of distortion.   Love to meet the guy ,without seeing the  record, who could pin point the null points with his ears.

Now you are talking 10mm which is  a pretty good distance.   If you have  reasonable math/ engineering  skills you can go to vinyl  engine and use there calculator  to see if you can get 2 null points and where they would be  using the 240 and  250 mm  mounting  distance.   Then maybe take  a record that  did cost 100.00  and try it  at 240 mm.  

I do not know how  involved  you wanted to get  but  thought  I would give you the option  to be able to understand  a little bit  of what is going on.  There are  guys on other forums  who will do the math for you or  run the calculators for you.

Enjoy the ride 
Tom