You can try and find a non-running truck and use it. You'll need to keep (and have working) the transmission. Other than that, you get in the scenario where you have to engineer everything from the bottom up and I can't offer advice on how to go about that; I imagine it's as difficult as it sounds....
I'd love to buy something part way there and not have to build from scratch, but the closest I found was a gas powered kit truck on a Ford Ranger donor, and I'd hate to pay full price on a running truck to then rip 1/2 of it out. And the kit manufacturer passed away this year.
If I don't go that route, I have lots of questions:
Do fiberglass bodies need aluminum reinforcement panels?
Can I use a light truck that EV kits are made to fit as a donor for chassis, transmission, drive train, etc?
What are street legal requirements and how do I get a VIN # and title a vehicle made in 3-4 different shops?
I'd love to talk to electric truck owners, especially those who've built something from the ground up.
As for the EV bits, sure. You can take a kit and put it in. The only part that might be challenging is the motor mount. You'll just need a torsion bar to keep it from turning and something to keep it immobilized, but I don't know what kind of mount points you'll have on a kit car. If the kit was made for a light truck, and you're making a truck that will be light, it reasons that you'll get the same performance, kit or not. Your top speed and max range might be curtailed a bit with a classic-styled shell because it isn't as aerodynamic, but by and large the weight will trump that. I don't expect you'd get significantly different performance putting a kit or your own assemblage of parts than you would in any modern truck.
I can't answer any of the fiberglass/aluminum questions. I know some like Pete have had to replace things like belly pans, maybe that will give some insight.
To get a VIN depends on your local authorities, but in general, you have to present a BUNCH of receipts showing that the majority of the vehicle is accounted for to ensure it's not stolen. You give these to a DOT inspector and they will issue your vehicle a new VIN. You'll have to contact your local DMV/DOT on how to go about getting the inspection done.