Depending on the markings on the rest of the parts, $1200 might be the value of the gun parted out. As a whole, I would expect it to sell for under $1000 due to the seeming mishmash of parts. An all original Underwood would price greater than $1200 if there was documentation so a refurbished parts gun with possibly slight premium for the Underwood name would be its overall value.
M1 carbines are one of those instances where the sum of the whole can be less than the sum of its parts depending on the parts. Underwood produced less than 10% of all M1 carbines so there is some value there regarding parts. The more parts marked Underwood, the greater the potential value to those trying to restore their carbine to original condition.
