Now that we know who we're talking to, let's proceed with engine swap dialog.
I expect that you are one of those people (and I have known several in my life, including my Dad) who are project oriented. My Dad swapped a Model A engine into an Essex in the early thirties. I expect that the fact that the engine currently in the car is expensive has little to do with your desire to do this engine swap. You want to do it because "it's there." I have done a few engine swaps over the years myself. If you have done them before, then you know what's involved and what you're getting into. Most people who talk about doing an engine swap haven't a clue what they're getting into, that's why I was discouraging before.
I still hate to see an MB get modified like this, but I expect you will do it regardless, and if you do, I would like to see you be successful at it.
If you are not totally hung up on a small block Chevy, a small block Ford would be a much more practical swap for this application. The sump is in the front, AND the external dimensions are slightly smaller. There are also oil pump pickup/oil pan combinations that can move the sump into different locations. But, I expect that using the pickup/pan combination from the sixties, early seventies would put the sump where you want it. This would be an easy item to find and will fit on any small block Ford up through the mid nineties when they went to what they call the Modular V8 which is a totally different animal.
Additionally, with the Ford distributor in the front, I expect that this would make things easier for this swap.
You also are not limited to the 5.0, although it is clearly the most common. The 351 Windsor is of the same family and would offer more low end torque, if that is what you want. If you're wanting to really build some torque and power, you can get an intake manifold that will allow you to use Cleveland heads. The Cleveland heads certainly outflow Windsor heads and they even outflow decent sbc heads.
Keep us posted on the project,