What you have there is a # 6 Traxcavator & they were based on a D6 9U tractor with the loader attached to it.In my area here there were some in operation but weren,t too popular like the smaller HT4 was.It was replaced with the 977 20A in 1955 still with the D318 engine & the 10A came out in 1953 so was only made a couple years.