On my 49 Chevy, you can hook a cable to the pawl (IE small lever) that operates the door latch. It is part of the door latch assembly. Take out your latch and look at it. On mine, they had a cable that ran to the inside door handle. The handle has about an 1/8" hole in it. The place to hook the cable on mine. Then run the cable through the door cavity. There should be a hole for wiring. Then run it through that hole and into the hole in the door jamb. See where it could exit to the front fender well. That's how it goes on mine anyway. By the way, you can get Stainless Cable from the hardware store with cable stops. Just make a loop to grab the end with your finger under the fender well. The hardware store also has large SS rings that would work well for something to grab on to.
Almost forgot. Use multi strand wire for flexibility.