I recently scored a 1974 Reading Company Summer of Equipment on E-bay. Expecting a simple roster, I was surprised by the treasure drove of information it contained. The document lists everything that moved on the Reading 1 January 1974, locomotives, freight cars, passenger cars, RDCs, MU cars, cabooses, trailers, company service cars, and marine equipment.
For cars, not only does it show number, class, and quantity, but dimensions, weights, coupler and truck type, load restraints and special loading devices, underframe cushioning, builder and year. The locomotive sections gives all the vital stats on the units: horsepower; weight; tractive effort; maximum/minimum speed; air brake type; fluid capacities; builder and year; dual/single controls; etc.
It turned out to be a GREAT resource.
Nick