i've got an old 225 1988, i know its 101 years newer than yours but sill runs ok
My mates a yamaha main dealer, problems with 300 big time, usually top two pistons?I know of one 300 engine which has had 3 new powerheads from yam and its only 1 year old.
And they only dyno up at 275!
All my V6 yams have been pre 1998 and i've had no problems,
gaZ