The Douglas C-54 Skymaster was the first 4-engine transport in the USAAF and probably saw the most service among the 4-engined birds. The C-54 was the subject of a Design Analysis [ HTML ] article in the September, 1944 issue of Industrial Aviation. So far, I have not been able to obtain a copy of the foldout color cutaway rendering from that article, nor from the reprint in Flying.

The DC-4E, from which the DC-4 and C-54 were developed, is considered to have been the inspiration for the Japanese Nakajima G5N Liz.

The Skymaster, being the largest transport in regular operations, garnered a few articles:

Additional Information from Technical Orders
AN 01-40NU-1 Handbook Flight Operating Instructions