67 Yenko Camaro engine question?

[dons67]

Anybody know what block casting numbers these 67 427's were? Some say they were 942 blocks others say 351 blocks. Were they 2 or 4 bolt mains. The Span Inc document also stated that the automatics vers the 4 speeds were only 410 HP. What blocks werer these? Any help would be appreciated!

[berger]

don I go by the march 31st 67 nhra chevy specs blueprints for any yenkos after april 1st, the auto 427 nhra has hydraulic cam listed, it gives the intake number, carb number, piston dome hght, etc. all you would need to race it in stock class, interesting enough they list the alum head option only on a tripower stock, and no mention of the L88 till july of 68 specs, I assume harrell and yenko would set you up according to what class you intended on running so you didn't get bounced for having the wrong carb , ahra specs may have been more important for them in stock class in 67, just not sure?? I got from the harrell crew who were their then and know their stuff inside and out that it was an early block and extremely thick. I know that sometimes not all the old stuff made it out the storage rooms at gm and 2 and 3 yrs later they would go to the back and pull out some dusty stuff, could have pulled out 961 4 bolts L78s, and they were real thick, once they showed up in cars they could have safely bored them all the way over as the same casting was also used on a later 2 bolt 427, Ive read you can bore them to 454 bore if you can find pistons 4.375 big..

[berger]

don cylinder wall thickness is key no matter what size bore you go with, I know the early truck tall decks are some of thickest gm blocks they had to offer, you could deck it to nhra specs and bore it out and you should have a inexpensive thick cylinder 427...

[dons67]

Thanks for the info. One more question. Were the 67 427's
L-72 or L-71 blocks. How could you tell the difference? We they date stamped for 1967 or were they pulled off the line and whatever was available was used???