I've narrowed it down to these. In case anyone has one laying around. Trying to stick with tillers. 10hp doesn't require registration, it's never had a number on it. 25hp is max allowed per CG and I still like speed.
Mercury Kiekhaefer Outboards
KE7 Lightning Deluxe 10 HP 1947 – 49
KF7 Super 10 10 HP 1949 – 50
KG7 Super 10 Hurricane 10+ HP 1950 – 52
KG7H Super 10 Hurricane 10+ HP 1952 – 53
KH7 Super 10 Hurricane Cruiser 10+HP 1952
Mark 15 Rocket Hurricane 10 HP 1953
KF9 Thunderbolt 25+HP 1949 – 50
KG9 Thunderbolt 25+HP 1950 – 52
Mark 40 Thunderbolt 25+HP 1953
Mark 40H Thunderbolt 25+HP 1953 – 55
*Mark 55 Thunderbolt Ser# 831021 – 899949 40 HP 1955

*Mark 55 for the no internal combustion rule and might require help with an entirely different skill set.