by Follicly Challenged » 26 Sep 2005 16:26
The boys in the casting plant were in a "big hurry" in those days to cut labor time costs as 'Ma was damn near broke, hence frigged up numbers on your castings.
Your heads from the "96" at the end, "75" somewhere in the middle, are most probably 75-79?, or thereabout, 360 "J" castings. To be sure look at the exhaust flanges that the exhaust manifold bolts to, for evidence of air injection "holes" on the exhaust flange faces just below the exhaust port.
They work fine, basically the same as any other "J" type 360 casting head, which "any of them", "any year" , may or maynot be cracked in the exhaust seat area. You'll have to clean and mag any head you buy (even imported), to know if they are cracked or not for sure.
As for those particular castings being exceptionally "thin" , I haven't seen concrete evidence of that. They were prone to cracks, but that was more a product of their application in those years, late 70's.
Let me explain;
Chrysler engineering began introduction/targeting of higher peak combustion temps(hotter burn) to combat Oxides of Nitrogen production in the exhaust gases for emissions. (That brown haze over cities-SMOG)It was known at that time, that peak combustion temps above 2400 F reduced NOX production significantly, hence "ALL" manufacturers, not just mopar, were going there, to meet EPA standards for the time. Problem was they weren't initially revising the exhaust port designs to reduce heat sink in the valve seat areas with the extra combustion temp heat, which led to problems with cracking on all castings for many manuf's.
The above, was one of many reasons for the later 308 heads revised exhaust port as a fix. It's interesting to note that the 308 head retains virtually the same intake port as any "J" head from any year, 'cept slightly tighter as it passes the pushrod relief. The 308 heads crack also !
Sorry once again for the rambling/trivia, I seem to be an "almanac of useless information", as the wife calls it.