7 segment binary to hex

Find what museum is missing their 74xx logic ICs and return them. Then get a small microcontroller and do all this in a single chip. As a bonus, you'll be ready for other advanced projects from the late 1980s and beyond.

Maybe, if you feel particularly adventurous, you could even use a diode ROM, with perhaps two 74'138 3-to-8 line decoders to decode/drive the stuff. :)

Here's a crude schematic of the whole contraption; If you happen to use some highish efficiency LED displays, you may even be able to drive a common anode one directly.

The '!EN' pin can be either of the gate pins of the '138. You can also connect both of the other gate pins together, letting you turn the display output on or off as you please.

This also has the benefit over the suggested ROM solution that it's inexpensive to build/prototype if you have the parts on hand, or can't be particularly bothered to program ROMs.

Besides, one could even call this fun to make :)

If you want to fiddle with gates, another possibility is to use a small FPGA or CPLD. You can get started with a flash-based FPGA for a few tens of dollars.

Reprogram it as many times as necessary to get it right, and you generally get a lot of I/O pins per dollar.

Example VHDL code here

For example, (shaky and not quite a complete loop, but you get the idea):