[Dan in Pasadena]

Kevin, It's traditional here to introduce yourself and describe what your project intentions are - or will be when you buy a truck.

Others will chime in and our advice will vary but you can rely on 99% of the guys here trying to give you good advice based on their experience.

Front Suspension
You can make the I beam axle ride dramatically better than when it came from the factory but that said, it will never ride as good as modern IFS. Many here - myself included - originally intended to update their trucks using the stock I beam with disc brakes, power steering and lowering only to find out they would spend as much doing that as putting in budget-conscious IFS system.

From your photo is looks like it has only two leafs in the spring pack up front but they still have a decent arch. Thats good! Any chance they are Posie's Super Sliders with the formed pocket for a Teflon button? If so, those are some of the best if you're going to stay with the leaf spring setup. If not, you can have the springs re-arched by a good spring company to change the height to any you want. At least yours is lowered without the springs bending the wrong way! We've all seem that many time and those truck ride like crap.

Last piece of advice and it's strictly my $.02. Many use Mustang II derived kits with success but in the end I opted to use a Flat Out Engineering cross member for C3 era Corvette components. I still have an in-the-box new Fatman Fabrication MII kit I bought 2nd hand because I felt the Vette suspension would be a better choice for my purposes. Others will disagree.

Rear Suspensiopn
I'd agree on a rear end swap. You don't want adapters if you can avoid them. What do you plan on doing with this truck? Daily driver? Drag race? Canyon carving? You don't need a four bar setup though they are in vogue right now. You haven't mentioned wanting it lower or using air bags - many do use bags, I opted not to because I don't want to deal with crawling over driveway openings or speed bumps and the advice I was given is bags ALWAYS leak eventually.

Doors
Too bad your doors were hogged out. Many will make the same suggestion: Find the best used original doors you can. The reproductions don't fit very well nad will require work. Some much worse than others. Most originally are getting costly and the bottoms will be Swiss cheese or will require you to remove and replace with new metal in and out. Do you weld? It'll save you a lot of money doing all the rust repair yourself.

Fenders
Same advice: Find useable originals and make required repairs yourself.

Bed
Use the search button here. There are a number of good threads on the subject of making a long bed into a short bed.

Anyway, good luck with your project. I'll be interested to read what others advise.