I've done this myself, found parts and wiring harness bits in scrap yards. For me the biggest issue would have been going from no PDL's or PW's and finding the correct door panels. Luck was with me in that I was simply transferring both systems from a sold van to a keeper, door panels included. This transfer included the entire wiring harness inside the door, found the mating ends in the scrap yard and supplied my own interconnecting wires.
I did rely on an EVTM from the donor van's year to make sure things were wired correctly.
A 12 VDC power supply was needed so I installed a buss fused but active at all times---this worked great for the PW's since they're usable without turning the ignition switch to "run".
FWIW and YMMV this A1 AutoElectric outfit is someone I'd be very skeptical dealing with. I ordered a set of their power actuated dead bolt locks, what arrived was not what was shown at the time, a parts missing. Their replies were to the effect I didn't need them anyway, they had no replacements and I'd have to make do with what was sent. (They have since modified their website to show what I received which still hits me as a bit underhanded and after-the-fact.) Finding the same damn thing from a seller in the UK sent to me free for about the same US dollars and receiving what was pictured makes those locks just plain awesome.
Anyway if I can lend any more info I'd be glad to do so---PM me if you're impatient!