Using very small directed flame to heat the back of drop out but not glowing hot, leaving adjusters in place... I would be incrementally squeezing the bulging sides of the dropout( protecting itfrom teeth) in the jaws of a big metalworking vise to original width, but leaving the dropouts in the vise as I worked, spreading the drop out open slowly. No matter which method I used to spread it, I would perform the two actions in conjunction.

I am a fan of tapping a fine tapering cold chisel or elelephant sized screwdriver into the mouth of the dropout. (Shaft of tool in line with chainstay.)




Good Luck! Eric