I have an MG500 on a Laborator 1000. The 5x4 kit has the mixing box and an adapter plate that sits in the bottom of the head to make sure the box is located centrally. Each mixing box has its own adapter.
I can dig it out (it's in storage with the rest of my darkroom) and send you some pics if you like?
What the above post calls the adaptor plate, and I call the Register Plate, is the same for every every enlarger, fitting in the slot at the bottom of the 500 Head; they come in 3 different sizes of central aperture for the 3 different sized boxes. So 4x5 register plate is the same for every different enlarger for which adaptor kits were made. Not so for the box, however.
You were absolutely right about adapting plates for mixing chambers, so thank You all for info.
I've just received one box from ONE GREAT APUG forum MEMBER — Thank You very, very much Mike.
The only thing I have to do now, is making plate (which is lifting the mixing box for 4 mm over the bottom of a head) and start printing.
Best regards for all,