Scotty's post was the best answer. However, I'd add that if the op wants to glass bed a stock, buy a used one that's already been altered, like with an addition of a recoil pad. I wouldn't glass bed the original 300H&H stock. There are guys here that believe the pre 64 model 70 doesn't need glass bedding, but there are multiple reasons to glass be a barreled action into a stock. The op states one of the most important reasons to glass bed a rifle. Also, my take on pre 64's with the forend screw found on the standard weight models. The ones I have had, have shot most accurately with the screw removed and the barrel freefloated. That is of course after a proper glass bedding. That is the only way they are going to shoot accurately and retain the same poi year after year. With the forend tension screw, you are always going to have to check to make sure your poi hasn't changed, due to changes in humidity and different barrel to stock contact. Also, if the op's rifle is shooting that poorly, I'd remove it from the stock and check for cracks. If this is the case, all bets are off and I'd fix the crack and glass bed the sob...
