I was kind of afraid of that with all that top end wear like you described , when my Brother blew the 86' 350 the top end was in good shape , but the engine was running a little rich because he didn't keep the airfilter clean as often as he should ; i kept telling him change the oil and oil filter and as dry as it's been this summer in Ga. we need to clean our air filter's after each ride ! He might have blown it anyway the way he rode it , but it wasn't smoking or using oil ; so we will never know for sure ! Well since you have it torn down i would check out the bottom end as well , check the teeth for roundness an the lob's on the cam shaft and the rest of the bottom end as well as the main bearing's while you're at it ; since you've already spent the money for the top end if you plan on keeping it ! If transmission and everthing else is good , like the tire's and the quad look's good ; then it should be worth finishing the job ! ..........