Oldwiseman
The USRA locomotives are not the only ones that shared similar boilers. Locomotive weight is limited by axle loading restrictions based on track structure and bridge capacities. Since a 4-6-2 and a 2-8-2 have the same number of axles they can support the same boiler with similar axle loadings. Look at a Pennsylvania K-4 Pacific and L-1 Mikado and you will see the PRR used a common boiler design for both classes.
It was a relatively common practice for railroads or commercial locomotive builders to use a similar boiler design on locomotives of different wheel arrangements but with the same number of axles. Some common locomotive types that could share boiler designs are 4-6-0 Ten Wheelers and 2-8-0 Consolidations or 4-8-2 Mountains and 2-10-2 Santa Fe Types.
Sometimes railroads reused a boiler when rebuilding a locomotive to a new wheel arrangement. The IC rebuilt 2-10-2s into fast 4-8-2s. The GN did just the opposite and rebuilt 4-8-2s into slow but strong pulling 2-10-2s.
Sometimes model train companies use a one boiler on multiple locomotives as an economy measure. Sometimes model train companies use the same boiler on multiple locomotives because the original locomotive builder did so as an economy measure. 
