308 heads

I have a set for my 340 rebuild. They flow about the same in stock form as the older X-heads, but they have a better exhaust port design ( taken from the W2 heads) and lend themselves well to porting.They also have an improved chamber design vs the earlier heads. My set, with a stage 2 port, now flow 264 cfm at .500" lift, a touch better than stock edelbrock heads. Plus they already have hardened seats. They can be opened up to 2.02" intake valves pretty easily as well. They tend to crack, but not as badly as some of the early magnum heads. And of course you'll need to block the smog ports.

73cc's isn't the right chamber size though, typically they're 65-68cc's. Mine checked out at 65cc's. :-D