When John D was working on developing an engine for the early 4 cylinder Tempest and the folks @ IH were lopping off a head for the Scout, a secret group of engineers at Chevrolet were working on an engine for their soon to be released Nova.  However, the decision to make the 153 CID in-line 4 was more in keeping with the Chevrolets more conservative leanings.  While the experimental block was probably scrapped, this may very well be the valve cover from that fated engine...or not.