So I'm adding fake cassette decks to my MCM/70 reproduction and you might be wondering why. Couple of reasons. 

First of all the YUCoM software that I am using emulates a machine that has two cassette decks. When I visited the the York University Computer Museum Zbigniew Stachniak (Ziggy) mentioned that MCM did ship a model with no cassette decks (and one with a cassette deck and a modem), but that without cassettes the machine was basically just an APL calculator. So I could have saved some time and still been historically accurate I guess. 

More importantly though, virtually all of the online images of the MCM/70 feature the two tape deck model. It's important to me that my reproduction is clearly recognizable as an MCM/70 so placebo cassette decks it is.

Here is the result of my efforts.

 Based primarily on this photo and the measurements that I took at the museum.

I even got the tape eject lever working ;-) I still have to laser cut the acrylic windows for the lids.