Brownells has parts pages for other Rugers, too, including three versions of the SBH.
Maybe one of them would be more suitable: http://www.brownells.com/schematics/Ruger--mid109.aspx
It's also possible that the pictures don't match the actual parts.
Maybe a phone call to find out for sure.
It is the FIL's gun and he is kinda impatient with this swap. Even asked if I could make one. Everyplace that I've looked they are out of stock. I have a few more places to look.
SBH hammers are in generally short supply because a few years ago SASS (Single Action Shooting Society) legalized grafting the SBH hammer to the Vaquero and New Vaquero. So basically modders want 'em . My NewVaq has worn an SBH hammer since 2005.
Ron Power at Power Custom makes a hammer/trigger set that is basically a drop-in high-end action job, and last I heard he was going to expand into an SBH-pattern.
They have the Bisley kit in (but re-worked so that it can be added to, among others, the SBH):
I would call them and see if they have the SBH setup yet but it's not (yet?) on their site. Assuming of course you're OK with the increased cost (owch) but also bolting in the equivalent of a $125+ action job...