i ride trails and i think thats a lot of motor for just trail riding.. my 350 does just fine and holds its own drag racing with the 450's and raptors.
if you need the biggest baddest trail motor and have all kinds of money then by all means go right ahead. i have trouble beleiving you can use 80hp in the trails though..
if your crank itself is still good then true and weld your crank with new outer bearings, get a pancake bearing and a good clutch, have the cylinders ported, find an adjustable timing plate, either get a coolhead or have your stock head modified.
this should take you from 40hp to close to 60hp.. plenty of power for a trail machine. imo