What is this pair of heads?
 

I was rooting around in the chevy. head core department of my stockpile of stuff and came up with two cylinder heads. One of them is a 3946813 number, the other is a 3917 13.The 8 is missing on it. One date code is an E 5 1.The other head is an L 8 0. They are in the classification guide as a legal replacement head for the 327 250 horse head for a '68 Chevelle or big car. I have never seen any other heads with this number, one of them I got off Ebay about 15 years ago, the other one was from a core pile at a local machine shop that is long defunct. The heads I always ran on my Chevelles was a 290 casting, a one year only casting.It only came on '68 327 250 horse engines. Another casting was the 293 casting, and these came on 327 210 horse 2 barrel Camaros only. What is the origins of the 813 head as to its OEM application? I know all these heads are 56 years old by now, but it would be interesting to find out about the OEM application of the 813 castings. Any ideas?

Re: What is this pair of heads?
 

69 to79 350 smog head with 76 cc chambers.

Re: What is this pair of heads?
 

One thing I forgot to mention in my first post regarding those heads is that they have 1.72" intake valves. I don't know of any 350's with the small intake except a set of truck heads that had 11/32"diameter intake valve stems and 3/8"exhaust stems.That must have been an attempt to stop the excessive valve guide wear caused by the lower lead content of the fuels back then.The 1970's sure were a mess as to the effects of things on the automotive industry.

Re: What is this pair of heads?
 

Thanks to Barry Polly
https://www.ncrs.org/ok/LIME_BOOK_2018.pdf