The cam is good to 6,000, corect springs, valve lashOk. I know the heads from the 305 are worthless and I did a minor porting job, didn't really take much off. I guess the best solution is to spring for better heads. I know when I ran a tri carb set up with 3, 250 cfm carbs set up with progressive linkeage, when the two outer carbs open, the 305 really took off and rev up with no problem. Theonly reason I changed to a 600 edellbrock was I had a warped intake and it sucked the oil from the valley so I was blowing enough smoke to kill off all the bugs for a mile around me.