340 Identification.

Even if you decide which way you want to go with a "future project", it may be derailed until you actually tear the engine down. You will see what you have then. Block may be cracked. Ring glands melted. Crank may be beyond saving. Only can tell by inspecting it after you open it up and see what you have. Stroker kit later will open a lot of options, since its not original to any of your vehicles, hence resale value.
Just take a look inside it, and then decide. Build it your way and dont worry about being original after 40+ years. And by all means , have fun with it!