Re: 1959 johnson s/h qd20
Search this forum for 'fuel pump conversion' or '2-line conversion' etc. Lots of info. I still use the pressure tanks w/o issue after replacing coupler o-rings and 5/32 fuel lines under cowling.
Any 18, 20 or 25 prop from Johnson/Evinrude from '57-mid '70's will fit. You can likely get a new one here at iboats.com, or a used one at a salvage. My favorite is Tim's outboard 218-682-2331. They'll ship w/credit card FAST and very $ reasonable and knowledgeable. Just have your model number handy so they know exactly what you've got. Good luck!