those gt40 heads are still smogger heads... best way to do it is cruise ebay for a deal like i did and pickup a set of 302 H.O. heads with roller rockers and guide plates already installed for $300, then get them ported and polished and you got it.. or if you can fun some tunnel port heads... those really flow good... but they had problems with the pushrod enclosures breaking, and then oil going straight into your vavles