I was just reading the GMC speed manual by Bill Fisher. He mentions boring the 270 out to 3 15/16 to come up with a displacement of 292 cubic inches. For the 302 he reccomends a 4 1/8 bore to give a displacement of 320 cubic inches.
I might have to go back on the 302 pistons... the 4 inch bore may be wearing those cylinder walls a little bit thin.
