Still the rivets are going to be the not so fun part but at least the holes will be there already.
Having been planning a model railcar that has over 2,000 rivets, (EBT's M-1,) we've investigated many different ways to deal with them.
Archer has some decals that are raised resin rivets. They aren't as raised as 'real' ones (the ones with hemispherical heads) but they are easy to install. Archer will make up a custom sheet of decals, so you could get them already spaced for the 6500.
Grandt Line and Tichy Train Grp make plastic rivets on sprues that you just glue in the holes. Very easy to do in styrene. They are designed for HO and O scale, but with up to 0.08" head diam, they are a good [< 1.6"+ or less than 1.6"+] prototype rivets. I've had some success using an inkjet printer to print rivets layouts on styrene - you need one with a straight-thru paper path, like my Epson Stylus C88+. With a scanned drawing, you can make up a riveted side and print it on the styrene, then drill the holes and pop in rivets. Alternatively, if you have a drawing, get it lasered with the rivet holes already cut (see www.thegalline.com/
This photo shows Grandt Line rivets at the top (in laser-cut holes that are too big,) with Archer decals below around the window.
Here's one of GAL's CNJ cars with lots of rivets. (Alan likes rivets! Not sure how he made these, but I would email him to ask if he wants to make the sides for your 6500. www dot thegalline dot com.)
Finally, as Matt says, Scale Hardware sells real brass rivets that you can nsert and glue or solder.
Edit: This looks fine when you edit it. Not sure why the HTML shows - if it doesn't clear up I will re-insert the pics tomorrow.