I got the Harbor Freight impact driver and that and an application of heat finally broke it loose.
To protect the wood grip I wrapped the entire grip in five layers of aluminum foil. I took a knife and carefully removed the foil from over the screw. Heated the screw with the mini torch then used a tight fitting bit in the impact driver.
Once out I could see no reason why it was tight. The left back strap screw also need some heat to loosen it. Again no reason. Maybe Mario or Luigi put some extra muscle into it.
Thanks again. Other than those two screws this is one of the best fitted Pietta's I've owned. Bolt was only .001 wider than the smallest cylinder slot. The bore is really bright. Can't wait to get to the range on Sunday.
Thanks again for all the help!