Remember he's a salesman.
Don't buy anything until you've had your engine dyno-tuned and you have a benchmark graph of your TQ/HP numbers to work from. Then you might want to ask your mechanic for a quote on the labor to put on the new heads, assuming you bring him the new heads and the new gaskets, etc. Then you might ask him how much additional labor he would charge you if you also brought him a cam to put in as well. I know you're reluctant to do change out the cam, but just seeing the labor cost numbers wouldn't hurt.
