Ideas for you that worked for me
Sold My Boat is 1990 75 Hp 18 ft .
I had 500 hours on the big motor .
I put on a 1988 9.5 Honda in 1992 to use when Trolling .
The Honda did a great job but could not handle all the electrical I had so I added a GM alternator 82 amp this just about killed the small motor and it needed a 12 volt feed to excite the alternator.
If I did not disconnect the alternator the battery die over night .
I went the Repair shop and the fixed this alternator so it had magnets to excite and lower the charging rate to 20 amps still works great after 19 years and always starts on second pull.
I guestimate we have about 7,000 plus hours on the Honda saved a huge amount of gas no repairs needed on either motor .
New plugs and oil and fogged them before putting away .
This is the only motor I have ever seen with an added alternator.
It needed a new belt every year about $6.00.
When I told people what I was doing they said it would never work fortunately I did not believe them .