basically the process involves getting  a source of crankcase pulse   to  run the new fuel pump.

changing the side  fuel connector  (find out beforestarting your project)

hooking up the new side connector to the pump inlet   and the  pump outlet sent to the   fuel inlet   where the old hose  was.

you can use  the  old  pulse nipple feeding air to the old gas tank but you must modify the   flapper  valve  behind the   carb base  plate.

gets tricky but not hard to do. never done it on a  RD  but most likely doable….

look at this video on a smaller engine   same  principle.

https://www.youtube.com/watch?v=FtG4M7ye1N8

one simple method is to plug the pressure nipple shut  carefully remove and    drill   a .25  hole  in a bypass cover  center  and tap it for a nipple (Apply red locktite to threads)    this will provide pulsing for the pump via  a  new “pulse hose”  to reach the pump’s  pulse nipple.

hook it up to the  fuel pump pulse nipple  and hook up the in-out fuel lines desc. above.   see  example  picture  of  a tapped  bypass cover

Another   method on a smaller 10 hp FD  is to drill  the bypass cover and fit a drilled  /16th aluminum plate (with a hole behind the pump)  plate & mount  pump & gasket  over it…if it fits under the cowl

pictures are just a guide  you will need to  adapt the pump but it is all the  same process

• get a  crankcase pulse to drive the pump
• hook-up the pump
• change the side connector to single line.

suggest you download the bible  for your RD maintenance and  clear pictures.. book covers oldies from TN JW cd ad fd rd   maintenance

https://watercraftmanuals.com/outboard/johnson/manuals/johnson-302231.htm

thanks FR  for the update. I should have looked up UTUBES… so easy !!

1957 Johnson 35 Hp restore and double to single fuel line conversion (youtube.com)