75 olds 455 power adders
 

I have a 75 olds 455 don't know mileage runs OK slight tick cam or lifters maybe. Just seems under powered, its all stock, has J heads on it which aren't very well liked I guess. Don't want to spend a lot on it, would switching to a older set of c heads be any better than porting polishing the old heads with new values n seals? Thought about swapping the cam I would like to hear a lobe but don't want to kill the low end torque any idea what size can would be ideal? Also intake and carb I am running the stock qjet and cast iron intake, would a aluminum high rise and a 750 holley or edlebrock gain any more HP or torque? Plan on going through the top end and leave the bottom end as is