Back to the OP - I have several Ricks ranging from 1974 up to 2010 and there are some differences. In the earlier models - the 4001 had a weaker neck and the dreaded/loved capacitor which cut out some of the power of the bridge pick-up. The 4003 models have removed the capacitor which makes the bass more powerful sounding, but some pine for the old school vibe of the 4001. Models made since 2006 have a switch so you can go for the old or new sound. Neck sizes have changed over time - the 4001 was a bit thinner, then the earlier 4003 models were a bit thicker and in recent years (since 2006 or 2008) the necks have been made a bit thinner, but not like the old ones. All 4001 and 4003 models have both mono and stereo output. There are some other models like the 4001s and the 4003s which are a bit scaled down from the 4001 and 4003. The bodies don't have binding and there is no stero output. I have found with my 4003s that the neck is much thinner than on the 4003, but I only have my one 4003s as a reference. As a general matter, if you've got the money, I'd suggest to go for a new one from Wildwood, Pick of the Ricks or similar discounted provider.