The EF suffix code was only used on Chevelle big blocks in 1966. There are three models of Chevelles that the engine could have been installed in; SS396 coupe, SS396 convertible, or the Custom El Camino. If you was going to do a title search to try to find the original vehicle that the engine came out of you would have to reconstruct three possible VINs for these three models. However, Flint did not build El Caminos in 1966, so the engine could have only come out of a coupe or convertible.
The 702 oval port heads are correct for the 1966 360HP engine, and the 325HP engine also in the Chevelle.
Edit: Also be aware that an EF coded engine probably would not have been installed in a Fremont built SS396 or El Camino. A 360HP 396 in a Fremont built car would have most likely had a smog pump and then the engine would use an EJ suffix (4-spd, Holley, A.I.R.). I added this because I noted in another post of yours that you wanted to ship this engine to California.
66 El Camino 396/325HP 4-Spd
My Build Thread:
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62 Corvette 327/360HP (original RF engine and Fuel Injection) (future restoration project)
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