You are right, this is not an original receiver / barrel combination. Underwood made lots of replacement barrels to be used as spare parts. Underwood was finished making carbines before 8-44. Any chance it might be a 3-44 where the "3" looks like an "8"?

Was this from the CMPicon sales in 2003 or those sold to clubs before that time?

Any way, it looks like a nice receiver with crisp markings from the picture.