Very neat. First one of these I've ever seen. They must not have made too many of them.
The more I look at it the more I realize that not only was the casting done poorly, the clean-up machining on it is pretty rough too! It's interesting that they copied the reinforcement rib just below the hammer pin from the stamped version.
Please try to post up the whole gun at some point so we can get it into the Arsenal Component Configurations section Pat! It sure seems like a unique one to me!