you're awesome with the pics slick1. lol
i am not sure where the one on my 94 is but the one on my 89 was to the left of center up close to the rad and on top. fo sho.. plastic and it also had a phillips cuts in it. pretty sure it was in the upper hose... hmmm.
i actually rarely burp any of my vehicles. normally i just fill and make sure to put some coolant in the reservoir. i have never had any problems but the screw thing is the proper procedure.
just checked slick's pic and it wasn't the a/c one. more towards the other side. near the outlet from the t-stat.