The status as of now is that the operating arm/wedge and the belleville washers have been removed on both calipers, the piston has been removed on one caliper. So you have the plunger rod sticking out of the inboard end of both calipers, and they are frozen to the aluminum body of the caliper where the plunger passes thru and the small o-rings makes a seal.
You do need heat and press force, but if the tools you are using are the aforementioned heat gun and c-clamp, I think you are guilty of bringing a knife to a gun fight. The mass of the caliper is too much for a typical heat gun to heat up to any effective level, and the c-clamp can't generate enough force to matter.
You need more heat and more pressure to push it out. As in oxy-acetylene torch and a shop press.
The other consideration is, what kind of damage has already been done to the bore by this level of corrision? Not to mention the damage from forcing the plunger out? Will it be able to seal again upon re-assembly?