The premade switch box is called the "options panel" in technical jargon and comes complete as a kit (part # 57K1944, SMID: 147-1982-303). The "kit" consists of the housing, front panel, a wiring harness, knockouts for the tach and all but one switch, and some metric screws. No switches or tach are included.
The housing attaches to the top of the heater with 8 screws that go into threaded holes that, incidentally, should already be present in the heater assembly.
Mine arrived without any pem nuts or rivnuts in the housing to accept the screws from the panel. I had install my own rivnuts in the housing and change the hardware to SAE.
My intention is to build a custom panel for all my lighting options plus a couple of USB ports.
FYI, I ordered mine from a vendor that was asking a certain price. When I explained that all I cared about was the housing and offered something much less, he accepted.
PM me for details.