If the focus ring goes 50mm beyond the infinity mark, then the focus stop is already removed... It should give you more than enough back focus, possibly additional 10cm +.
The optics may have been relaxed as well (or it doesn't need any intervention) - try with high power eyepiece (5-10mm), the astigmatism (if exists) will be visible on stars, at 100x and higher magnifications.
Have a look at what I am doing about focus here:
http://www.iceinspace.com.au/forum/s...124#post991124
The main issue is backlash..