Perhaps balancing would take place during assembly, after piston and rod weights were known. At 2500 rpm, it's probably less critical than our cars. The shot peening process will harden the surface a little. 37-50 hp. probably means it's not highly stressed anyway.
All cranks are balanced to a factory standard to be used with factory rods and pistons. You buy an aftermarket Eagle or Scat crank, they usually come pre-balanced for factory parts. I do know that the Eagle 302 Ford crank MUST be balanced per Eagle. Yes, people usually balance the motor when "Gee-Whiz" parts are used, but not necessarily when the rest of the rotating assy is stock. As far as the shot peen goes, the surface compaction will work harden, but only to a depth of a few thousandths. When the crank is ground, any work hardening is removed. The peening process is for cleaning and conditioning anyway. The journals for diesels are either flame hardened, nitride hardened, or hard chromed. When a diesel crank is ground, the factory usually specifies that it needs to be re-hardened.
