Looking to buy a horn but can't find any info on how to tell the difference between the 6d and the 8d.

Serial number tells me it's a conn made in '79, but that's it. Any help would be appreciated...

It's been a while since you posted this so I'm not sure if it's still relevant, but check out this older thread: http://www.8notes.com/f/51_234349.asp

I believe on the 6D the thumb trigger valve will be set almost in a straight line with the other three valves, while on the 8D it's set further back. This might be the easiest way to tell. Compare the 6D (http://i.ebayimg.com/00/s/NzIwWDExNjU=/z/8jwAAOSwDNdV61Bw/$_1.JPG) with the 8D (http://www.kesslerandsons.com/wp-content/uploads/2015/11/horn5.jpg) *Pictures don't belong to me

The 6D is pretty distinctive with three bigger valves for the fingers and then the noticeably smaller thumb slightly offset but almost in a straight line. With the 8d the smaller trigger valve isn't in the same line at all but well above the line of the note valves. There are other things about the wraps but that is the easiest thing to see quickly.