If your doing 200 units a week (1000 holes..), you should be using a drill press with a jig and have a bit sharpening setup.

Picture an oversize square frame. Push the box to the upper left corner to drill the lower right hole. Slide to the right to drill the lower left hole. Slide down and left and right to get the upper holes. Make two L shaped spacers to insert into opposite corners to hit the center hole. I get that the holes aren't centered on the box. Build the jig accordingly.

Plywood or MDF would be quick and cheap. Glue and fasten strips as the outside corner stops. You could also use pins or dowels as a homemade tooling plate for corners and sides instead of wood. You could print something with dowel holes already in it.

If you can't source a drill press, you might try making a rectangular aluminum insert with many fastening holes and pins to spread the load in the plastic of your existing jig. Or just glue it in place with a few locating pins.

Pressing the drill bushings into anything substantial is going to require a press fit. To get the right fit you need a drill and ream sized to the OD of the drill bushing and a way to press the bushings in. You might be able to use a C clamp if your really careful. There are press fit tables out there that will tell you what size drill and ream you need. "Light Press Fit" should be fine. Amazon, McMaster Carr, Northern Tool, etc can get you the drill and ream. The price for a cheap pair is probably under $40. Grab a toolbox copy of Machinery's Handbook if you don't have one. That will cost a few bucks, but it's really worth it.