The only modern ad on on mines is the electric fuel pump and a couple of inline filters, while my tank doesn't leak it does give off a steady supply of fine rust particles, so I have filter in front of the electric pump and another up by the engine to catch anything the first one misses, both of the filter are the old style that you can take apart and clean out,I keep a can of brake clean in the glove box in case it dies while out running around, I jump out remove the filters, blow them out and I'm on my way, I've cleaned my tank a dozen times and no matter how good it looks I still get rust!
As for mirrors, when I got my half track it had a CCKW mirror arm welded to the side of the of the cowl, I'm not sure when it was added but since it is a WW2 era mirror I just assume it was done by guys in the field when the realized you can't see squat out of these things! I also have a big clip on mirror that I clip up above the drivers seat for moving around the yard or driving into town, then when I'm in a parade or showing it I can just take it off and put it away out of site.