The link below appeared some three years ago so it may be old hat to some. It also may be teaching Granny to suck eggs to others, but it is worth a look as it is informative, especially if you are after a R4 but are not too familiar with them. The more info on what to look for the better I feel:
http://www.classicsmonthly.com/files/2010/09/r4.pdf
Regards,
ChrisH
http://www.classicsmonthly.com/files/2010/09/r4.pdf
Regards,
ChrisH