The first of these saws was made by Reed-Prentice in 1946 and the last in 1949. They weigh about 85 pounds. I doubt that one man could use one very effectively. Every one I've seen, including the one I own, has a bar about 36-37 inches long and a helper handle on the end.
Reed-Prentice has a long history in manufacturing, beginning almost 140 years ago. The company goes back to 1872 when it was A.F. Prentice & Co. F.E. Reed bought the company in 1877, the same year A.F. Prentice joined two other brothers to form Prentice Brothers Co. F.E. Reed retired in 1912 and the two companies merged to form Reed-Prentice Co. They have a long history of manufacturing woodworking machinery, including lathes and mills. Today they make plastic molding machinery. Originally located in Worchester, MA, R-P is still in business today in West Springfield, MA.
They made the very earliest Wolf chainsaws from 1927 through 1940. In addition to the R-P model 1200B, they made the Reed-Prentice Timberhog and the R-P model 50. They made pneumatic chainsaws during WWII and after. They got out of gas-powered chainsaw manufacturing in 1953 after McCulloch, Homelite, IEL/Pioneer and many other companies flourished onto the North American market. R-P decided to go back to their basic manufacturing strengths in lathes, mills and other industrial machinery.
The R-P 1200B was made with Reed-Prentice nameplates, and also badged for the Sears-Roebuck Company with the Craftsman name. There are still a few dozens of these 1200B saws in existence today, including some in good operating condition. The cylinder and piston in the McCulloch-made engine are round.
One curious feature of the 1200B's is the hollow bar. There are channels within the bar for oil to travel through to various points in the rail channels to lubricate the chain. The very earliest of this model had a spark retard lever for easier starting and adjustment at different rpms operating speed. This feature was discontinued in early-to-mid 1947. The fuel tanks are pressurized at priming and during operation. A metal plate on back of the powerhead gives starting and operating instructions.
There's a long discussion thread of the R-P 1200B chainsaw in the chain saw collectors forum History section. You have to register in that forum to be able to read it.
If you want to get one in memory and commemoration of your father, you should talk to BillG... He might be willing to part with one of his.