I've seen places that offered this on Pontiac heads before. While porting me heads I really started thinking, there is no reason other than maybe cost that I shouldn't fill my exhaust crossover passages. Can only increase my exhaust side flow(and we all know thats a good thing on a Chevy especially a 383). Can I do this myself? Maybe buy block filler from Summit and fill them up after sandblasting out the carbon? I know block filler is really for waterjackets so not sure that would workout. If I pay to get it done, about how much will it run me?