In this weather your Sprinter just won't produce heat at idle or low speed. Its not the van. You can try an idle stick to bump it up but that's not economical. Can't help with the rest, good luck.
Well they do, and I have no idea if a jeep engine set up in a north south position (which is what your original post was talking about) would be an easy swap into a fwd version when the exhaust manifolds are part of the head.