That is cool. Just for kicks, before you start replacing "consumables" just rebuild, clean and lube everything. I recently picked up an '85 620 missing only the rear Derailleur. If you haven't used 1/2 Step plus Granny gearing, read up on it a bit and ride the stock bike as is. It's pretty brilliant. I've got 700c wheels on mine now but I'm going to give the Matrix/Helico 27 inch wheels a workout when I get some tires.
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I don't do: disks, tubeless, e-shifting, or bead head nymphs.