If you can buy it, don't build it.

1/4" stainless is way overkill. The stock plate is ~ 16 G cad / zinc plated steel. V8 motors had a similar if not exactly the same plate.

Have a look at a South Atlanta based MB dealer, they have parts manuals on line. The part exists but MB sometimes has a strange way of listing parts.

I did find a cover for the hole in the oil pan / bottom bell housing area 120 014 00 33 $ 10.00

The dual starter mounts are for left and right hand drive cars. The starter was moved to passenger side to make room on the drivers side for the steering box.