Dyno Don's car that night was first door slammer in the 7's , but we were told a 429 with aluminum wedge CJ heads. Dyno probably had more than 429 cubic inches, ( everyone else did) .
Yah know, you may be right!
He had been running, at first, the all-aluminum 351C based block in match race trim only as it was not allowed at the time in NHRA rules. In IIRC a SS&DI magazine article , Don was depicted holding an empty aluminum 351C block at waist level in the pic to show how light it was (98lbs. IIRC).
But, I now also remember a a 385-based match race engine using a Can-Am aluminum block as well.
Not sure now and I cannot find any reference a to which engine series set the 7 second record.
Edit: Found it! It was a 385 series big block per this article.
http://www.competitionplus.com/drag-racing/news/3770-dyno-don-nicholson-15-mmps-all-time