OK. There are a few different aspects. I prefer having the switches to switch the ground/polarity and lift, etc. Which complicates that.
It is very easy to build a a basic A/B/C/D box and you can find schematics easily. If I had more time at the moment I would happily build you one. But for the foreseeable future I don't have the time.
Radial Engineering makes great stuff and I have a lot of their products.