Many of the changes in the 1300s were quite logical and progressive...
The muffler was required because the line runs past houses on the climb up from the wharves. The size of the muffler was determined by the need to avoid increasing back pressure which would decrease power.
The projecting radiator on the rear resulted from a modification to DE8 and DE9 (which had no rear walkway as built).
MKA just adopted these two changes, and built the new body around them.
It looked odd but it was what the customer wanted....
DE2 doesn't look exactly like it did now with a new cab and nose as T414.