The original driveline components are no higher friction than components available today. If they feel that way, it is because they are dirty and have ancient grease in them. With any luck they would clean up nicely and have good bearing surfaces.
I think you might end up being rather put off by the total cost of components to upgrade these bikes to modern standards.
I would suggest one of two routes: look into overhauling the bikes as they are now, or look into buying all new bikes. I highly recommend the former, but then I have my biases.
jim
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Cross Check Nexus7, IRO Mark V, Trek 620 Nexus7, Karate Monkey half fat, IRO Model 19 fixed, Amp Research B3, Surly 1x1 half fat fixed, and more...
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SB forever