My brother had a 375 Marlin for a while. When prices started going up he sold at a handsome profit. He could do even better today. Those guns have gone crazy in value. It is worth a lot more than the 300 WSM. If you don't want to use it, sell it. But this isn't a fair trade for you.
I actually like the 300 WSM, but not in the FWT stock. They used sporter barrels in those cartridges and they just look WRONG in that stock.