I quickly perused Mr. Nugents link. Another point came out that is in favor of the fit of a small Ford. That is the oil filter on the Chevy interferes with the steering box. The Ford oil filter is on the left front of the motor in a better location for the swap. The Power Steering pump is also in the same spot as the MB's, I would use the Ford pump and simply adapt the hoses.
The Ford alternator is also in a convenient location for wiring. I expect the a/c compressor is also in the correct location. Any of these items can be moved anywhere there is no interference, but is much more easily and cleanly accomplished if they are in the same location.
There may be some GM loyalty here that is disallowing the Ford engine as a possibility in spite of the practicality. I since that because of the 3.8 Buick suggestion. If you're dead set against a Ford V8, speak up and I'll stop pointing out the practicality of it.
Everything else being equal I would prefer an SBC because of the wider availability and interchangability of speed and replacement parts, but the if the fit of a Ford is more practical, the Ford engine is a very good engine. There again, sometimes brand loyalty will prohibit such thinking.