I noticed that aluminum heads and blocks do not become available until 1970, but i know that production engines had them before hand, for example, the Fiat Twin Cam I4 had an aluminum head in a mass produced engine in 1959. Aluminum blocks have been around since 1915 for mass produced engines (hispano-suiza V8 aero engine) and even the wright brother’s used an aluminum engine. Even the first car Enzo Ferrari made outside of Alfa, the Tipo 815 used an aluminum engine. I think aluminum engines should be available at any year like OHC just very expensive for heads until the 60’s and blocks until the 80’s.
Currently you’d need to invest quite a bit of money in research to use alloy heads and blocks pre-70s, which represents the fact that its quite difficult to build a reliable aluminium engine, but if you’re willing to invest the money, you can