You should measure the barrel length carefully. These could be had with barrels in 1/4" increments and the 4 1/4" variant is very uncommon. IIRC the very last prewar .357 Magnum shipped had that barrel length.
Pardon my nosiness but how did you manage to come up with a prewar Magnum thinking it was a Model 28 Highway Patrolman? Neither seller nor buyer could have known what it was or the price would have shocked you.