Remove Stabilite Lens

[70sWagoneers 17]

What is the standard operating procedure to remove lenses from antique head lamps that have no removable bezel. Im working wit Stabilite headlamps, that are probably from the early 1930's. One lens is broken and I see that the inner reflector assembly is sprung and moves in about 1/2". So far, I cannot figure how to get the other lens out. The lens is generally about 9" diameter. The glass is bigger than the lamp housing opening. There are three notches out of the housing at the bottom of the lens opening and Im assuming that these are key to getting these ships out of their bottles. The lens Im trying to get out could be a prior replacement that is oversized perhaps and I could use some advice on that scenario too (heat gun the housing to get it to expand). 

 

Thanks

James C.