Center console shifter opening

[Rrrockhound]

My project to retrofit heated seats has hit a snag in that the opening for the shifter in the center console wood trim from the donor car (a '92 S124) is larger than the opening in my car, a '91 W124 sedan. The opening in the donor car's panel is 89 mm x 134 mm, and mine is 81 mm x 121 mm. I need this panel because the heat switches are in it. Another user has offered to sell me a panel from an '88 W124 coupe, but it is also the larger size.

Complicating matters is that I want to also fit a manual trans. So maybe it won't matter. So I guess I have 2 questions:

1) Why is my car's shifter opening smaller than those from both an older car and a younger car's?

2) If I do the manual swap, which size will I need?