Wondering if it may be one of the change over blocks when the '67 Novas were converting away from the L79 327's in preparation for the 350 conversions. One of those '67's is around here somewhere, a series of them built in April - June '67, P-O-P coded as an L79, with a apparently original 255 HP block (or 275 block - help me, DW) - I wish I could remember the casting number. I'll look for the article describing this -
Regards,
Steve