Having owned Browning/Miroku guns all of my shooting life I have seen a variety of stock bolts used. Some were a roundhead with screwdriver slot, bolt. Others have been a 12mm socket headed bolt either with or without a screwdriver slot and latterly a hexagonal or allen key headed bolt. Can I suggest that you remove whatever heel plate or recoil pad is fitted to the heel of the stock, then using a bright torch, shine that down the stock bolt hole. That should enable you to determine what type of stock bolt is fitted. When you are removing the bolt and you feel it go loose, take it back a couple of turns and then tap the screwdriver/socket extension smartly in the direction of the action. This will release the joint between wood and metal. Do not forget that IF your gun has the long tang trigger guard, you will have to remove the screws in that first. If you are not confident in doing this, take it to a gunsmith. The MK60 should have the short trigger guard tang though.