Paul,
I'm not an expert but if true 6" (not 6.5) on the 29, then it likely is newer (80's???) model which may not mean a whole lot on your trade.
Can you post pics and/or more details (box, docs, tools, grips, etc)... something more than just barrel length of the 29?
The dash number, the condition make a lot of difference in both guns. Usually the older but pristine models will have more value than the newer versions.