That would be a fairly early MK VI (doesn't help the value as the best guns were considered to be made after the 17xxx range, but it really doesn't hurt the value either). If you had a box that would add to the value. The MK VI came with either the walnut slabs or the Pachmyer or both grips. I think most of them had a flat black Pachmyer mainspring housing, don't think I've ever seen a MK VI with an arched housing but its likely there were some. Other models seemed to have either mainspring housing, I've got 4 of the MC guns in 9mm, 2 have flat mainspring housings and 2 have arched. They were pretty flexible in the factory with building guns to customer wishes. BTW, the pistol rug itself is worth about $45.00