What is it?
 

Can anyone identify this engine? The only mark on it is "51" which is stamped on one of the mounting lugs.
What manufacturer? What time frame? (I suspect late 1940's to early 1950's, but let me know if you know more.
Any information would be appreciated! Thanks!https://cimg7.ibsrv.net/gimg/www.rcu...525a65953a.jpg
https://cimg0.ibsrv.net/gimg/www.rcu...2fd1946a7f.jpg
https://cimg1.ibsrv.net/gimg/www.rcu...40338d0e97.jpg
https://cimg1.ibsrv.net/gimg/www.rcu...0240d4d36c.jpg