Chryco is 100% right. The 308 exhaust ports are far superior to the old X/J heads. Looking at my old flow figures it looks like the 2.02 heads flowed about 15 more CFM than the smog 1.88 heads on the Intake side. 215cfm~ to 200~ Seeing how you can easily get 250cfm+ from a 1.88 head if you just install the bigger 2.02" valves and do some porting it makes little sense to go out of your way to find them. The 308 heads with the hardened exhaust seats and superior exhaust ports are the way to go.