Allot of that depends on what parts you will need? If you are fabricating various pieces to the running gear then you could upgrade a bit and find newer suspension parts, rear ends, etc. to build into the running gear. I thought you were talking more about components like hoods, windshields, doors, dash knobs, things that are specific to the COE design... Surely there must be a good local welder or fabricator in your hometown? Sit down and talk with them and start taking measurements so you can get some idea of what newer components will work. Also, start hitting the local towing yard auctions, you never know if a newer model 1 1/2 ton or bigger wrecked truck may come in, that may be your running gear!

what if i have a ceo i just need custom fabrication and parts or where should i go to get custom parts

COE's are getting tougher to find these days, used to be some in a junkyard close by but most of the big stuff went away with high scrap prices and I can only imagine allot more are disappearing quickly every year. Farm country is going to be your best bet, you may be able to find an old retired truck still sitting on a farm somewhere? I would start spreading the word and hitting the streets if this is a project you want to do...