there are plenty of instructional videos on the web for this sort of thing. however
if your '84 is friction shifting yes you can use the same housing for the RD. you can likely use the ferrules from your current cables on the new cables.
Idealy a ferrule should be used on any housing end. the assist in ensuring the housing is straight in the adjusting barrell or housing stop, therby reducing friction. just look at your current setup and see where they are.
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