Welcome to the PY forums !!
Run the XE-274. You might want to port the combustion chambers.
The 670 heads are closed chamber and don't like running on todays gas !!
If you call me I'll walk you through the procedure.
1-303-776-0877
I also offer the Comp cams, LOWEST PRICES out there !
Take a look at my web site:
http://www.pontiacengines.net
Click on cams.
Thanks,
Pontiac Gregg