Originally Posted by Paul Goutiere
I'd be a little cautious if you have to cut the wood. There often is sand embedded in the wood grains and it can raise hell with even a carbide blade.
Washing the wood couldn't hurt, as long as this doesn't take away from the look you are trying to achieve.
As for the archival treatment you may want to line the rabbet with "aluminum duct tape" from the hardware store. This will effectively seal the wood from the mat and mounting board.
Lineco makes a "Self-Adhesive Frame Sealing Tape" (item L387-0151) just for this purpose. I use it in the rabbet of all the wood frames I make.