Besides spring perches, the shock mounts and brake line tabs (all part of Chris' kit) will need to be welded on. You'll also want the e-brake cables from the donor vehicle as the Sterling cables differ from the van's stock rear cables. I think Chris' e-brake adapter is meant for the Sterling cables, as well. I'm not sure, but I would think the speed sensor connector should plug right up on the pumpkin. At least it did for a 2003 Sterling into a 2003 van. And of course, gearing should match front and rear.
A question for Chris: Does your install kit include the brake line coming down from the frame with the T-block on it? If not, DJM, you will need to get one.