Aladin, I started building cars before any of the modern suppliers were in business. J C Whitney, Speedway Motors and maybe a couple of other suppliers were all we had. I remember walking through a wrecking yard and thinking I was in heaven, because I could adapt many later parts to my old Hot Rod. In the 1960's I was a TV repairman who built cars as a hobby. My degree in electronics made me serious about wiring my cars. I knew every Mom & Pop auto parts place in Dallas, and was allowed to mix-and-match radiator hoses, fan belts, vacuum lines, PCV fittings, brake lines, etc. because they understood I did not know what car the part may be from that I would put on my car. Those were great days. I have no idea how many cars I have built or helped build, and I learned a lot of tricks from other builders. Never be afraid to ask and copy good work. Factory ideas also can be adapted. Pre-fitting things to a body or frame saves lots of time and makes things look neat when finished. It often seems like a lot of extra time but it makes life better later. Believe me when I say driving through Podunk Arkansas in a Street Rod with a different motor, trans, steering, brakes, and much more, at 2:00 AM can be a big worry. Where do I go if something brakes? Knowing electrical problems are a major factor in on-the-road brake-downs, having proper wire size, fuses, circuit breakers, relays, and "safe" wire routing, makes for a nice worry free trip. It is always a good idea to layout wires in their general area before actually installing them. You may find some items are not where the harness thought they would be. It is much easier to modify a harness laying on a garage floor than after installed. Good Luck!
