I'm running a 1992 30 HP Evinrude short shaft O/B on my 1958 Lone Star Nassau (16' Aluminum). It maxes out at 25 mph. I'm looking for a little more top end, so I'm trying to locate a 35-50 HP short shaft motor. Are HP ratings the same, regardless of vintage? Assuming good compression, would a vintage 40 HP motor (e.g Big Twin) really push more than the 1992 30 HP motor, or does improved technology get more performance? (For now, I'd rather stick with existing motor than go the jack plate route to let me run a longer shaft.) Any other considerations? I'm finding that 40 HP short shaft motors are actually hard to find. Thanks much,