You really want to allow 9" x 12" x 5" high to get in common baby AT boards with the cards and their brackets, so 4.3" is a bit low for that, you'll have to cherry pick cards that are a little below bracket height and de-bracket them, or use low profile cards and brackets. Then you've only got a couple or three inches width for PSU, you might get an NLX form factor one in there, with ATX to AT converter.

In general, if you want a yet to be specified build in THAT case, you can pull it off.. but for general casing of AT parts it's a bit tight, and a collection of parts you've already got might not be ideal for it. It's a get the parts that fit the case project, not a case that the parts easily fit project.

I don't know if I need to note that it won't take full length cards either, you need 14" for those and that's if the bracket is flush with the back panel, not inset. To allow an internal mounting rail and card holder rails at the back end, it's more like 15".... Also older boards, though still "baby" AT because they don't go on for another few inches past the keyboard hole, may need a full 14", particularly those like 286 with a lot of socketed RAM, or first generation boards of 486 or even Pentium, where they don't so much have a chipset as an extremely large set of chips.