At least part of the reason for mounting the engines "backwards" was for streamlining. The leading edge of the Peacemaker was swept, and the engines were 28 cylinder R-4360's with 3800 hp each. For the propeller to clear the leading edge, the engines would have had to be mounted forward of the leading edge, much like the B-29's, which is an aerodynamically dirty design. The trailing edge is almost perpendicular to the fuse, so no problem with prop clearance. The wing section of the B-36 was so large that there was an accessway inside the wing that the flight engineer could reach the engines through.

I always thought the B-52 was a big airplane, saw many on the ramps whenever we flew into Carswell, but the B-36 absolutely dwarfs them.