That is a fine heirloom piece you have there!
I've done some business with Mr John Harrison and he has my eternal respect.
I've yet to invest in any custom work beyond the stuff I do on my own, but were I to do it, he'd be at the top of my list. I've got his ignition parts in a number of my own 1911s, and now use his True radius jig for seers.
P.S. If I'd looked at it more closely, I should have identified the slide-stop and sights as Harrison from the get go.