cables and tops
on what i'd call the rear end of the cable, there's a spring and a ring terminal that gets screwed to the aluminum top frame. the other end is riveted to the header at either end. be sure that you use a properly sized flat washer on the inside of the fiberglass header so that when the body of the pop rivet expands the flat washer keeps the rivet body from expanding so far that it damages the fiberglass. there's a fair amount of tension on the cables and i've seen some hack jobs where someone used a self tapping screw instead of a properly installed rivet and broke out the ends of the header.
all the verts had the same standard top from gm, something like m20. and they all had exactly the same hardware except for a change in the strap fastener for the floating bow directly above the rear light (window.) the older cars had a chrome snap on the strap and the later cars had a friction tab, a sort of clamp to lock the strap in position. i prefer the older snap as the plastic clamp self destructs.
i was trying to figure out the termination on that cable from your pic. i know that it's not anything i've seen and i've done a bunch of metro vert tops.
the rollers in your pics appear to be some hardware store replacement. they're definitely missing the plate behind them that has the keepers bent into it.
my rollers were cracking apart on the last top i did. i was on a trip to my local hardware store for a2 stainless and i found a drawer that had replacement rollers for sash windows, the ones that have weights in their frames with ropes. they had quite a selection of rollers. i found a couple that had the right diameter and ball bearing centers but were a little thinner. the ball bearings' inner race was too small for the shoulder bolts for the originals so i just replaced the oem bolts with a2 ss button head bolts with blue loc-tite on the threads.
the action of the top on my red vert is smooth as silk and i can pull it shut with one hand.
a couple of those online top joints sell the proper cables. i used to see them on ebay, too. i think that i have been generally luck to have owned cars that had decent cables so that i didn't have to change them out. from the factory, the cables had a nylon coating so they didn't fray very often.
there's a convertible supplement to the fsm from gm. about 4 pages of generally useless verbage and a video supplement which was supposed to be a part of the gm tech training on the metro. the video is really a short section, 1 of 4 tops discussed, and is pretty much devoted to the actual adjustments made to the frame. unless the frame has been sprung or twisted, you don't have to make those adjustments anyway.
a picture tutorial on top replacement
the deal with the vinyl tops is that the rear windows are heat seam welded and there's no material to overlap when you try sewing in a new window. you have to make the window bigger and generally it looks like shit on a white duck, i've seen some.
on the top, function is only half the battle. appearance is important, too. the top on a vert makes or breaks the look of the car.
the sewn in, zippered windows on metro tops that i've seen have a border that overlaps the zipper. from an appearance standpoint, it hides the zipper. from a functional standpoint, it keeps water from leaking through the zipper.
the zippered window adds $75 to $125 to the cost of the top. the value would be that you could replace the window more easily. i think the sweet spot would be a stayfast or german sailcloth top with a zippered window but then you're talking about a $500 to $600 ragtop plus installation.