Let's see...40 plus year fuel tank. Buy some plastic drums, remove fuel, slide out tank, clean, add some brocade refill and move on.Fuel polishing? Just a catch term. Two fuel filters on GM's are fine for 50 plus years. Change secondary every other time.Those new style filters can be useful for the newer engines, but an unnecessary expense on yours.
tank is not that difficult to remove if you can access the 12? vertical 3/8 capscrews that attach the cross bows to the side channels. Through the fuel door, you can remove bolts that secure the filler neck to top of tank. If the floor access panel is still there above it, you extract the filler neck assy, disconnect fuel gage wire and fuel line. Then slide tank out drivers side of coach. Empty is best. Hard to remove layer of sludge and dirt from bottom otherwise, due to tank baffles, which are at every tank strap. Straps are not disturbed during removal, BTW. I did my tank when switching to the 165 gallon one. Was significant crud on bottom. Fuel is pretty clean nowadays compared to years ago at stations.