The MCR2 regulator is not only taller it is also bigger in the other two dimensions. You can actually force an MCR1 lid inside an MCR2 lid, and the MCR2 lid usually has a bulge on one side.
Ron
If you take an MCR2 base and carefully file along all four sides and radius the corners of the Bakelite plate the coils are mounted on you can fit the correct MCR1 lid and clip...I've bought the lids only at jumbles and the clip can be made from a stainless steel tig welding rod.....Ian