GMC 302 and 270H heads have not been a subject for this kind of modification. The port design is different from the later sixes, and for all-out racing applications the various aftermarket 12-port heads have long been established as the better investment in money and time.
As Larry has demonstrated, "lump ports" are not a modification to be undertaken by amateurs. The process of installation is intricate and unforgiving of error. Design and development of the "lumps" themselves has been expensive and time-consuming--and, occasionally, controversial. Good, large-port GMC heads are growing increasingly rare, making failed experiments even more expensive, for a market that would never be significantly large.
God's Peace to you.
d
