I would probably start here for the bracket/pedal mount: http://www.yogisinc.com/Detail.cfm/-...94/product.htm
For appearance sake, under floorboards, my opinion
, would be your best choice. Firewall mounts tend to create working space problems as well as just plain looking cobbled up.
I hope you are going to at least use front disc brakes plus improve the rears as this vintage Chebbie really has lousy originals.