Welcome Jon and I'll 2nd J Lucas' "nice truck" comment!
From what I know about 1941-46 GMC pickups, yours looks like a "long bed" version of the 1/2 ton. Zooming in on the rear axle hub, that is definitely a 1/2 ton rear axle. We can help you figure out more on your truck if you can provide pictures of the trucks make/model serial number plate(s). If the original it's still present, it should be located on the right hand side of the cowl (passenger side under where the hood overlaps the cowl). Should look similar to the 1st sample pic below. Yours may also have a model and serial number stamped into the right frame rail above the front spring as described in this great
GMC resource page.
After a bit of further web snooping and looking closer at your pictures, it looks like your truck is sporting a "Government" issued/assigned serial number ID plate as well. That's the additional plate circled in my zoomed in screen grab of your picture, followed by the screenshots from some other known originally government owned trucks.
I can't answer on your passenger door lock question, but perhaps some of our GMC gurus will chime in and offer more info.
Looking forward to seeing more pictures of your truck to help figure out what you have.
