I take it by Chevy 1500, you're talking about the 88-98 trucks? There's several issues with using that front end under an earlier truck. The first is , of course, the track width. It's going to be too wide for the earlier truck. The second problem, and really the main obstacle to using it, is how the suspension is integrated into the frame on the GMT 400 chassis. Unlike the earlier IFS trucks, the GMT 400 does not have a separate crossmember that the suspension mounts to, all of the suspension mounts are part of the frame. On the 2wd trucks, the upper control arms mount on top of the frame rail, 4x4s mount to the sides. In order to use the suspension, you would either need to use the entire front clip, or be very precise about transferring over the mounting points and welding them to the older frame.
However, there is another solution. I don't recall who makes it, but there is a company that makes a mounting kit where the AD body can be installed on a GMT 400 chassis. I believe they also make a kit that allows for the used of an Impala/Caprice chassis as well.
