There isn't a lot of dual wheel 4x4 trucks out there but i wouldn't call any square body truck "rare". There were over 15 million Chev & GMC trucks made between 1973 & 1987.
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I just did that, what a pia. I used bailing wire and pulled the wiring harness through. Take the drivers side visor off to gain more access & help to guide it through. Good luck.