Let me put it this way. I ran 11.82 with J heads on my 340 back in the late 1970’s so they can work. Would I use them today with all the aluminum head chooses available, NO I wouldn’t. I sold all my old heads off to a friend for 50.00 so I didn’t get any crazy ideas.
I'm not thoroughly convinced I'm going to see a very noticeable performance difference from my mildly ported 596 heads to the speedmasters that are imported... We shall see...