Welcome to the FGF site. My first recommendation is to have the car documented by Pontiac Historic Services (do a search on the web and you will find it). PHS will be able to tell you exactly how the car was built and what engine, trans, exterior color, trim levels and options the car had from the factory.
You can also decode the plate on the firewall on this site. It will tell you exterior and interior color.
NPD has pretty good stuff, as does Classic Industries and Year One. As far as quarters, they are available from a few parts suppliers - OER (Classic Industries) which are GM licensed, Sherman and Goodmark.
Unless your front fenders are just junk, I would stay away from the "new aftermarket" fenders right now. Too many negative comments on fitment.
As far as converting to a manual trans - a stock Muncie 4 speed is nice with no modifications required. If you try to install a 6 speed you will be required to modify the trans tunnel and fabricate a trans cross member. Bjorn (also on this site) can address the 5 speed trans as he has a friend in Houston who has one in his '69 Firebird and is not that happy with it due to the modifications he will have to make to install a console and the final drive is still 1:1 ratio.
Keep asking questions and I am sure many on the site will be glad to offer their opinions.
