That does look like a very good deal. I'm not sure about the NOS mods, but these are reversible so you can always try with or without.
In terms of modding the CD-63 (or any of its derivatives, of which there were quite a few), I started with the Acoustica mods which brought about a good drop in the noise floor and brought out more detail and made the whole sound more involving:
http://www.acoustica.org.uk/t/63/63hacks.html
Then I trawled through the pages and pages of info on the diyaudio website and cherrypicked a handful of mods. Beware that this link will take you a LONG time to trawl though and can become quite addictive:
http://www.diyaudio.com/forums/digit...mods-list.html
Be warned - Over 1000 pages of posts - sheesh!