I don't know if this cast bracket came with a particular speedometer as a kit or if it was sold as an accessory over the counter.
It appears that what you have is a bracket that mounts a Stewart Model 26 to a dashboard. You are holding the bracket upside down. The bracket places the speedometer far out beyond the dash making for a strange looking arrangement. There would have to be a hole in the dash to allow the cable to run to the transmission or front wheel. Hope this helps,