Hmm, ever intend to crop?
Practically, you could use your camera and a cold light back with the proper neg carrier set up on a copy stand or a sturdy tripod to make such a thing.
Alternatively a simple box of the right dimensions with a lens and light source in the right places hung on a wall bracket over the work surface. Projectors can be very simple.
Of course you have to consider how the cost of a good enlarger has dropped lately. Buy one now, use it and take care of it and later when they are hard to find and in demand by latecomers to the art of analog you can sell it for more than you got it for.