Quick check of Ancestry.com found almost a dozen William McClelands born from late 1850s and 1860s, so no chance of a match unless the name is recognized as a old-time shooter. The information in most letters for early guns come from a shipping ledger and almost always shows only the name for special orders and one-off buyers in handwritten notes. The records from the factory are only digitized back to 1920, so difficult to search for invoices, etc. for earlier guns. One option is to give the Historical Foundation the model, serial number, date shipped and see if they come up with any documents? There is a charge for this service, but may find more information? No charge if nothing is found is my understanding.
BTW, the factory would never do a refinish that looked like that one. Edges would be sharp, sideplate fit would have looked like it did when leaving the factory, and no dished pin holed.