It's hard to find info, this thread on mud seems to have a little info:
Chevy I6 and Toyota Engines | IH8MUD Forum
Wikipedia for the F engine also vaguely states some similarities but no sources. I had been told the engine was originally used for agricultural pumps that GM made, and then licensed the design to Toyota. I forget who told me that, it may of been from the Land Cruiser Heritage Museum or just some random guy online... though I've had a few people mention that the F engine is a rip off at a minimum of the GM I6. IIRC all the engine internals convert to round imperial units, and I think the fuel pump I used to have on my FJ40 was directly from a Chevy engine.
Anyways, most of that is me not remembering things entirely except from limited conversations with people telling me the engine has domestic roots, which the little info I can find online seems to agree with that haha
EDIT: Some other google searches brought up similar info, again all somewhat vague and claiming that the Chevy 235 I6 came after the 2F, that the 2F was a direct knock off of the 235, that Toyota licensed and ancient I6 in the 30s and that legacy carried into the F engine, etc.
F and 2F engines: Chevrolet influence? | IH8MUD Forum
True Origins of the F engine? - Pirate4x4.Com : 4x4 and Off-Road Forum
Toyota 2F engine - The Stovebolt Forums
Chevy's 235 and Toyota's F/2F/3F| Grassroots Motorsports forum |
https://en.wikipedia.org/wiki/Toyota_F_engine