His cut down rifle barrel is same length as the issue carbine barrel.  The rear sight is a 1901 rifle sight. The flat milled on the barrel is wider than the one on my original carbine barrel so my earlier thought that its a possible carbine barrel is incorrect.  I will post pictures of the barrel flat.  The M1903 sight band/base that I removed was milled to increase the ID to fit on the barrel. As a result the keyway is very shallow and no woodruff key was used. This probably contributed to the rear of the sight base cracking from recoil.  For the ease of front sight blade replacement/sizing I am thinking that a M1903A3 front sight base is a better choice for his rifle as it will never be mistaken for a legit carbine anyway.My plan is to reduce the OD of the barrel end to fit a stock M1903A3 front sight base  w/ the OEM woodruff key and retaining pin. 

Where are you from in MI??  I graduated from WMU many moons ago. Almost all of my relatives still live in the State.

Mark