Aftermarket wiring harnesses

[1968c15]

So I recently acquired a 1968 gmc c15. The body is in great shape but the p/o completely hacked up the wiring harness so I am planning on installing a new harness. I was wondering if anyone has used either the 28 circuit painless kit made for our trucks or the 18 circuit summit harness made for gm's. I've been getting ridiculous quotes for the install so I was wondering also how difficult it would be to install my self and how much time it took some of you. Thanks