since you are looking at doing a '50, it would have a split windshield, you could always split the cab and add to the width. the glass is flat so possibly easier to have custom made for you. that way you would get a wider cab for less of a shoulder to shoulder ride on the inside and possibly fit it onto whatever frame would tickle your fancy. you could custom build a frame as well. get some scrap i beam from a junk yard or whatever and build a frame stand and then weld up a frame to your liking from rectangular tubing. you could bolt in the front suspension from a 2wd '80's truck with disc brakes etc or something newer like a dodge dakota or a ford crown vic. whatever your width taste buds are craving. newer the better I would say because stuff seems to get better engineering wise for brakes etc plus parts are off the shelf at any roadside parts store if doing a road trip. try to keep the original wheels from the donor along with the tire size because this will keep the steering geometry correct as far as scrub radius and steering kingpin inclination angles are concerned. also the wheelbase is good to keep somewhat the same as the donor due to steering arm geometry. if looking for rack and pinion steering keep in mind how the steering column will fit to connect the dots from the column to the rack or box. if you buy a donor vehicle you could be money ahead in terms of stuff you will need like driveline, steering column, rad, heater/ac, brakes, park brake unit, seats, etc etc. if you use the floor from a donor you will have no problem finding a new carpet that fits like a glove.
here are a few videos with some theory on steering angles and references to other helpful videos that you should know before starting. google ackerman steering angles, or scrub radius, for starters. you don't want to build something from parts off other vehicles only to find they don't work well together as an assembly on your put together vehicle. that would be one reason to start with a donor vehicle frame and driveline. it was engineered to be that width and length. also, if using a donor, try to pin the suspension at the stock height with the weight of the complete donor sitting on the frame, using solid bars where the shocks mount for instance, so when building the old truck on top you will keep the suspension where it is made to be at ride height. then, when done the project build portion and before paint, remove the bars and adjust the ride height by increasing or decreasing the spring or using air bags or adjustable struts. this way you can keep things where they were engineered to be and the unit will ride and steer properly.
if you use a newer style vehicle you may benefit from having seats with built in seat belts. a bonus for a truck build that would have limited "strong" places to install shoulder belt mounts.
just a few thoughts.
https://www.suspensiondesigner.com/k...centre-offset/
https://www.youtube.com/watch?v=mh_BUOguZQk
https://www.youtube.com/watch?v=oYMMdjbmQXc
https://www.youtube.com/watch?v=IUcZ63unEyU
https://ismasupers.com/downloads/tec...steering-4.pdf