Wiring question

[av8tr33337]

I didn't get a response in the electrical forum so I hope it's ok to ask my question here. I have a 51 chevy PU and will be using 1984 305 carburated, 700R4 tranny, GM stearing column, possibly an electric fan. Down the road I may want to add electric windows, heated seats etc. I need something that incorporates everything I need in the chassis and under the hood. I am a do-it-yourselfer, but I'm not a "mechanic" I need something with clear instructions. I was pricing out a new wiring harnesses from painless for about $540.00, and found what appeared to be the same harness (painless)at Jegs for $300 and something. Are there any other vendors that you would suggest. I'm on a budget, if you could call it that,