Hi Andy I work on the motor case around the same size as the prop diameter, the rpm and power of the old motor. Add a few more rpm as we like to go faster. Matching the revs from the old motor e.g. 20,000. Kv of the brushless motor times the Lipo Battery cell number(4S= 14.8 volts) e.g. 1450kv times 14.8= 21460 rpm. So an OS40FSR was 1.6HP @ 20,000. Replacement 3648-1450kv = 21460rpm(no load). Power 750 watts = 1HP and the 3648-1450kv is 1600watts.
As for brushless to brush motors you can match the rpm, but, the brushless are far more powerful than the brush motors.
As for a conversion chart it would be a big task and some of the gear is not available in all countries.