Your instant center is a location. What location did you pick? If it's around the front bumper, and the upper arms end up at 5° down (at ride height), then tack it in. 5° seems a bit steep off the top of my head, but I certainly haven't done the measurements for the C10.
.... or did you use one of them 4-link calculators available online? If they say 5° and you're happy with the amount of anit-squat, giv'er. It may be worthwhile to make them adjustable - not a whole lot more work.
This is on my Pontiac Firefly (Chevy Sprint) (notice the forward mounts):
