Well I think if it was me I would start with the serial number range for a 1972: 3266263-3482752. Hit Marineengine.com and try and get part numbers for the things you need.
Then; armed with part numbers you can do a search on e-bay etc . Lots of those sellers have pictures of their parts so you can do a visual check against yours to see that they are correct.
If you haven’t already….run the engine first to whatever extent you can. Check for decent running, shifting, cooling etc. before you start spending money. Parts can add up fast. Lots of folks just hold off until an affordable parts motor turns up.
https://www.marineengine.com/parts/mercury-outboard-parts/110/3263263-thru-3795657
