The bike I have been riding for the last two years is a Yamaha IT465 (81 model). I just bought an 82 YZ490, but it needs work before its rideable.What are some of the significant differences in the way the engine delivers power? I may put the IT's 5 speed tranny with the 490's top end, or just swap in the whole 465 motor/tranny assembly. I'm building a desert racer, i ride at 7000-9000 ft elevation, I weigh 190 lbs. I have NO experience with the big 490 YZ motors, but I sure do like the stump pulling 465 IT motor. Anybody have first hand experience with both of these bikes? id really appreciate some advice.