I just purchased a 1948 M70 for a donor action. The safety is very stiff and hard to pull back to the first position. I took it all apart down to removing the firing pin spring and cleaned it out with a degreaser and compressed air and then reoiled everthing. The safety moves freely without spring pressure but when reassembled it is still hard to move back. I was hoping to disassemble the bolt sleeve to see what the problem is and possibly polish the camming surfaces. Does the pin that holds the safety lever have to be driven in completely and then retrieved when the firing pin is pulled back?

What you describe is a somewhat common problem to the M70 safety. What is most likely happening is that the cocking piece is not being drawn back far enough when it contacts the sear. One a Pre-64 Alaskan I have was so bad that the safety lever wouldn't budge at all. It probably would have broke of before it moved.

You can diagnose this by shimming the cocking piece by placing a strip (or two) of aluminum flashing tape on the sear and cock the rifle into battery. 0.010" pipe wrap tape works well for this too. Now check if the operation of the safety is any easier. If so you know this is your problem.

I would find a smith who knows the M 70 type safety well and have them fix it as a surface grinder is more precise than using stones. But since this is a donor action just have the safety timed and trigger repinned when you build it into a complete rifle.