I figured i'd repost this here in the Scarab section to see what you guys think. Add to this possible XR drives.
----" I am looking at a 90s' 38 Scarab (non- AVS) and was wondering what power to go with.I am pretty conservative and non abusive with my boats .About 35% of the time cruising at idle,50% of the time at 3400-3600 rpm and about 15 % at high speed 4500-5000 rpm in 3-5 minute bursts at a time usually.And low hours (about 10-20 a year)-I don't think I would be happy with 502 mags (i.e.415hp).So what is the best for -1)power 2)longevity 3)fuel economy in the 600-650hp range.I was thinking of 502 mags with Prochargers or whipple chargers (about 600-625 hp) .525 EFI and just deal with a little lower HP for reliability,or 572 GM and have them reworked for marine application(600-620hp).Or building custom blower power(which I always see as problematic and high fuel consumption).I Like 502 mags but want to go faster than 65-70mph.I would be plenty happy with 78-80.....of course until I get there and want 90.Thanks Mike G"

As always, depends on your budget but you are gonna need healthy HP to get a 38 to 80mph. Look for some used Merc 575s and you could always boost HP with a simple pulley change.

Years ago I was looking at a 91 with 540CI 600HP they said would run 80. I had a 89 with 600CI 720hp #4 drives that would run 80 no matter if Iwas empty or fully loaded,sometimes 85

this go's 81 on gps with pro charged 454s 698 hp staggered trs.1979 377