73 Buick running on 7 possibly 6!

I have a 73 buick century 350 sb. It has really slow acceleration (it lags) and drinks more gas than even a car like mine should. I took it for a tune-up and the guy said the car has low compression on possible two cylinders. he said i need to rebuild the pistons. I was wondering if anyone knows what else might be wrong that might cause that so i wont have to sacrafice so much money to rebuild the pistons.

thanks.

no, he said he has to rebuild the heads and all dat. Could re-ringing the pistons be the problem as well? Would dat cause lower compression?