The only part unique to the .375 is the barrel.
The trigger plate, butt stock,and squared lever from the 30-30 will interchange according to Gunparts Corp.
The price for the 3 items is approx.150 dollars U.S.+S&H.
The serial no. on the older models is on the tang part of the trigger plate. I don't know if that would cause you any problems.
The cheapest way to handle it would be to buy the 30-30 with
the features you desire and swap parts then resell the 30-30.
ppk665