Have a look over on HMEM forum, couple of scale models there and more of just the engine as well as a single full size engine replica. I have got part of the engine drawn up which is truer to the original than the casting kit or ready to run Chinese engines.
As I said I have only partly drawn it up and even the main “castings” are not fully detailed yet let alone all the smaller machined parts, and they are Alibre part files not 2D drawings. So bit to early to think about building from what I have. It does have the correct bore/stroke ratio and the cooling water can actually circulate.
I did some work at Mercedes Milton Keynes in the 80s. The atrium in their office building always had a historic car on display and while I was there the original Benz was rotated in. You could do worse than contact them, most companies are happy to help as far as they can.
This is certainly not the original Benz but I believe it is a later model. The photo was taken at Goodwood and it was part of the Mercedes display which included all the Silver Arrows.