as you have not had any other replies I have been thinking about having a go at the one that I recently got this is some of what I have found on the interweb hope it helps.
http://www.americanairgunhunter.com/crosman4.html
http://sites.google.com/site/cherryt...rosman2240mods
http://anotherairgunblog.blogspot.co...max-results=20
http://www.network54.com/Realm/CFTech/Bioportupdate.htm
Pat