A follow up.
The instructions said to line up the top edges of both doors, which I did. Once I got the center hinges installed, I noticed that the actual pattern in the doors don't align very accurately. It's probably off by 1/8". Which is annoying as frig, because the door is already a little short, and don't have the "room" to trim another 1/8" off the top of the one door.
Especially annoying, because these were two 18" halves of a single 36" folding door, that were shrink-wrapped/packaged all together in one unit.
But I'm also worried about the hinges. This kit is meant to hang from a top-mounted track, and the hinging action on the side being handled by a pivot pin. I'm not able to use that, which means I needed to cut some hinge mortises. In cutting them, I'm noticing that this hollow core door's structural perimeter frame is fairly soft MDF. I'm actually fairly worried that the hinge screws will pull out. I've already gone overboard and using 4 hinges instead of 3 so that should help in theory, but....ugh... do I maybe replace one screw on each hinge with a toggle bolt that extends into the hollow cavity, to anchor itself on the inside face of the framing? I really don't want to have to try to cut the MDF out to replace it with solid wood blocking... Ugh...