These were -92's with -94 cylinders. The only external difference on the airplane was the cowl flaps didn't go all the way around the circumference of the cowling, only the lower half.
Had the same arrangment on my DC-3. I was told it was the 'speed cowling kit'. Now how funny is that! As it was proven on the turboprop DC-3s, it only goes so fast and that is it.
The reason my old DC-3 was faster than other DC-3s I flew was, I believe, because of no de-ice boots and the fact it was so low time.