It will not be anywhere near "bolt on." The front frame horns are completely different - first gens have two carriage bolts through the front, second gens have bolt plates that go through the sides of the frame behind the bumper.
I have a first gen body on a second gen frame, and I did put a first gen bumper on it but it involved cutting frame horns off of another frame and modifying them so that it fits. It looks OK, the bumper should sit closer to the body though.
My suggestion is, don't waste your time with it, the first gen bumper will not line up with the second gen body lines and it will look funny. If you want a different bumper, build one from scratch that fits and looks like it should be there.