so maybe i can be of some help. i have been a certified mercruiser tech for over 25+years and can tell you this. mercury marine is making it more and more difficult to make rebuilding things affordable. i had a customer last year ask me to repair his shifting issues from past mechanics improperly adjusting his shift cables and causing the clutch dog to wear down the pawls on the gear sets which would cause the shifting to jump out of gear at low speed. i priced out just the foward gear and pinion set for his gen II's this does not include reverse gear because that is how merc sells them and it was $900 by the time i was done putting together a parts list together for just replacing the shift parts and gear sets i was way over $1700. this was not replacing any bearings, shafts or touching the upper or labor to complete the job and i couldnt warranty like mercury could. so i priced out brand new drives and found it to be more cost effective and gave my customer a one year warranty which i think he could extend i forget now. new drive was around $2400 from what i remember. mercury seems to want us to stop being mechanics and be parts changers instead. as far as high performance use not the greatest drive for that. yes i have seen them behind big blocks back in the '80's used on boats that where small and light and they would hold up ok but i also seen the same package used on single engine 268 sea ray and they would grenade due to the larger prop and boat loads being applied. granted these where alpha one/mr drives and most of the times the vertical driveshaft was the weak link and would snap right where the oring groove is at the top of that shaft. things changed when the bravo drive came out in late '89-'90's hope i was of some help. as far as heat/cryo treating gears i here from the performance guys they tried both and they still break gears. keep in mind all alpha type drives use helical cut gears which are weaker than straight cut like used in all bravo lower gears and only and used in the upper bravo xr drives