Everyone should own at least 1 FN Browning A5. As Shotgunjones stated the guns feel alive. They just work, I've got an early 60's Light Twelve 26" imp cyl that I use to hunt and fun sporting clays, can't seem to miss and gun handles very well.
Sound like the one you are looking at is pretty nice, here is a pretty long thread over on Shotgun World that may help you with a time frame and give you an idea what to look for. As far as price,799 if all original and excellent shape is an ok price, 50 to 100 bucks less would be better.
http://www.shotgunworld.com/bbs/viewtopic.php?f=53&t=216472

Picked up this one a few weeks ago, first year,all original,1903, serial 2182.