I straightened one many years ago. A friend had a jig in which the bottom metal was mounted. Key parts of the jig was a couple of pins that went up through the guard screw holes and a clamping system that locked the jig and plate together. The pins kept the guard screw holes in their proper spacing during forging.
Once set up, the front tang was heated red then forged flat with a large hammer. Once cool, the bottom metal was cleaned up with a file.
Also, the magazine box and the trigger had to be reduced in depth about 1/4". Timney makes a trigger that is designed to fit the flattened bottom metal.