[taylorpontiac]

I believe the engine to be a 65 chevy 283. Head#'s are "378450" there's also "GM 6T" and "18 78". Looking at the side of the heads, there seems to be a raised stamp that could be the double-hump? BTW, the engine casting # is 3849852

 

[DoubleVision]

3849852....283...57-66...2
376450.....75-81...262/267/305..6 or 7 exhaust bolt holes, 60cc chamber
I didn`t find a 378450, only a 376450, 6`s can look much like 8`s.
As for the symbols on small block chevy heads, it`s always on the front of the casting.

 

[taylorpontiac]

so would these be good heads on the 283? right now it's got a 2bbl carb/headers.