pfister shower valve removal - about how much brute force is too much / tricks of the trade?

I'm trying to remove a pair of pfister shower valves. I've removed the handles and flanges (or whatever the right word is) and now I'm down to removing the valves. I cleaned up with Naval Jelly then soaked with WD-40. One is surrounded with plumbers putty and turns a half a revolution or so then binds. The other one has no putty around it and won't budge with probably 50 ft-lbs torque.
Anybody know how much force is too much? Or any tricks? I hear mineral spirits or turpentine are good for softening old plumbers putty. For the other one should I use more WD40, Naval Jelly or what??
Thanks BC
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Bob Cooper wrote:

Chip out the putty and any grout that's in the way. If you can find a 1/2" drive deep socket (automotive) that will fit over the stem, use that. If the stem goes thru the drive hole, put a big pipe wrench on the outside of the socket. Torque away.....assuming that the piping or other supports will take it.
I've had a couple that were in so tight that I had to remove the whole valve body from the wall and take to the shop:-(
Jim
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