The loss in a manual transmission is significantly less than in auto's, refer heat losses (22% is a redicuously high).
A drivetrain loss thread may be in order. That said what do you believe the actual drivetrain loss to be on a stock Lexus? If the number is less than 22% that would make the first gen engines WAY overrated at 250hp. Using say 17% with a 175rwhp measurement leaves 211hp flywheel (250hp claimed). 17% on a GS400s recorded 235rwhp leaves 283hp flywheel (300hp claimed)