Put a newer transmission with that newer engine
I’m working on a few updates to my 1940 Dodge Pickup and I really enjoy your magazine. I put a higher-speed rear end in it from a 1972 Charger and an updated drive shaft was built in a machine shop. I also have a disc brake kit coming for the front end. Now I’m wondering if there is an adapter made to bolt a newer-style 318 V-8 to the original three-speed manual floor shift transmission? I like using the original-style clutch and brake pedals and three-speed on the floor and I’d like to retain that setup.
The vast majority of hot rod, street rod, and resto rod builders don’t want to do what you’re trying to do, namely bolt a vintage transmission to a more modern engine. Instead, they want to bolt a modern transmission to a vintage engine or install a modern engine and transmission. I could not find a source for an offthe-shelf adapter that would enable you to mate your 1940 Dodge three-speed with a modern 318 cid V-8.
If you’re willing to invest enough money, you can have a machine shop fabricate an adapter for you. As an alternative, consider installing a modern transmission along with the newer 318 engine and then adapting your pickup truck’s original pedals and shifter to the updated transmission. That would amount to adapting and/or fabricating clutch and shifter linkage, which might be easier and less expensive than fabricating an adapter plate to join your old transmission with a newer engine.