Looks like with the way the slots are arranged, you can only fit a card with dual-slot cooler into the x4 slot, and only a single-slot card will fit into the x16 unless you remove the PSU.
GT1030 are much easier to find in single-slot, and 30w (or 20w for DDR4 version) is much more likely to work with a 180w PSU than a 60w 750Ti
There are larger drop-in Flex ATX PSUs that would fit inside (such as the 300w from the Optiplex XE3) but then you still wouldn't be able to fit a dual-slot cooler card. There would be plenty of room for a cooler if you mount the PSU externally but if you had to do that, may as well get a standard ATX one.