ported 243 head vs aftermarket
Tfs 225 (pretty sure theres a small bore option) otherwise the 215s
Afr 210 or 230
Check the 235s I think they have a minimum bore of 4.030
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Anyway, look at a few of these options. Ballistic Speed has some ls3 heads with new valves etc for smaller bore applications, they may be worth looking into.
AFR 210 TFS 215 PRC 227
But you could potentially gain 20-30
Also go to ballistic speeds website and look at those reworked ls3 heads. They had a dyno of a 383 that put down over 500rwhp with them.
Go look. Now!
Most of these heads are bronze valve guides. You must use roller rockers or it voids your warranty. If you dont you will have premature valve guide wear. Now some do offer the option of powdered metal guides to run factory rockers. Factory rockers with the trunion upgrade are pretty damn good.
These heads start about $2300+

