Bill,
Congrats on your purchase. There aren't many 6700 around, or at least on this Forum. Unfortunately,
there is only one place to get manuals, which you can find on the post "Fast Moving Parts". There are a couple other parts suppliers listed in "Parts Drawings", but there are only three online suppliers in N America, unless you have a good local Yamaha shop. I don't know of any other air filters that work for these tractors, so you're kind've stuck there. The shifter guide piece is a pretty common replacement part, as they seem to break often. The only problem with these mowers is the parts supply, as they were only made for three years...
Rattosh51
YT6800