Looks like the harmonic balancer on the front is a single pulley and might be for a 7/8" belt. As you maybe noticed, the water pump is missing off the front. The valve cover has the hole just in front of the GMC logo for the PCV hookup and the oil filler just behind the filter has the oil bath filter for the PCV system. From the size of the filter housing I think your right about it coming out of a larger truck. The larger capacity filter was needed for such things as compressors and the larger hydromatics as the oil was run through these different components. Good candidate for a full flow conversion anyways
