I'm currently in the planning phases for a project to turn a 1990 Econoline Van into a moving sculpture. Part of the plan involves welding onto the frame of the vehicle (after removing most of the body). I am marginally capable with an oxy torch, but I'm curious as to what the best weld process is for this purpose.
I will be doing most of the work outside, but semi-enclosed, and the welds need to be fairly strong.
What weld process you use is not as important as the geometry of what you intend to make with the welding. Each of the welding processes, while having slight variations, works in basically the same way by generating some heat and melting the metal and then letting it re-cool. Whether you use some form of arc welding or torch welding (or electron beam welding for that matter), matters a lot less than how you treat your weld and how strong the surrounding structure is.
What may determine what you use may be the material of the frame. If its a steel frame then an oxy torch will be fine, if its aluminium, you'll first find it almost impossible to weld and you should use a MIG or TIG welder to keep the weld pool covered in inert gases.
Keep in mind that the welded patch of metal will be more brittle than the surrounding area because it will harden due to the local heat treatment, try and smooth off the area around the weld afterwards using a grinding wheel or similar to make sure you don't get crack propagating through the weld from any sharp changes in geometry.
That's quite a long answer but I would guess an oxy torch would be fine if you know how to use it.
I am marginally capable with an oxy torch, but I'm curious as to what the best weld process is for this purpose.
Are you looking for the easiest process to use to reach a goal of acceptable results? A properly adjusted MIG welder will act almost like an (electric) caulking gun for metal. Just squeeze and point. Pair this with CO2/argon mix gas for pretty welds. Add a $50 auto-darking helmet so you can see what you are doing and get up to speed the fastest.
The "best" process is subjective, but most professional welders can weld almost anything almost anywhere with almost any process. That said, the ones I work with clearly prefer TIG over MIG, and MIG over stick, and stick over torches.
I suggest you find someone to teach you whose equipment you can also borrow, and follow their guidance - there are enough variables left unmentioned in your question that it's not something we can answer objectively.
That said, Ford publishes the Ford Truck Body Builder Advisory Service, which provides their body builders book and specific information on each vehicle regarding portions of the frame you shouldn't weld, how to attach certain items, and some dimensions, wiring, and other information vehicle modification businesses need as they modify their vehicles. Included are the econoline vans, so you should find a great deal of information there:
https://www.fleet.ford.com/truckbbas/
Although I now notice that they don't have information on your older vehicle. There is still some general recommendations, and you'll find the dimensions and many other aspects of the van are very similar, if not unchanged, for later models, so it may still be a good use of time to visit that site and see what is applicable to your situation.
You can call Ford and request the earlier manuals, but they apparently don't have them digitized and online.
