My second floor circa 1980s tile shower w/ fiberglass pan is leaking. The drain appears to be the main problem, so I was hoping to use a wingtight shower replacement drain to fix the problem from above. I cannot remove the old drain. It's different than pictured. No rubber gasket, instead, the ring turned to be soft metal. I did manage to get that out. The PVC pipe is now freed up, but I can't get the remaining 2" (or more)metal collar out. It seems to be completely secured to the fiberglass shower pan. I've tried loosening the lip for the collar - that worked a bit-- and also pouring "goof off" under the seal. I did use a hacksaw to cut through the collar, but stopped short of making a complete wegde in hopes that the collar would collapse---as it just doesn't seem to budge. I do have limited tight access from below... have also tried using a hammar and crow bar to push drain to the surface.

Any suggestions?

The shower drain manufacturer of the original drain is FIAT. When the old drain comes out, it appears that the Wingtight drain will be a good replacement, but the Wingtight screen won't completely cover shower pan.
I could probably configure the FIAT screen to fit the wingtight drain - using a demel - but not sure that is a good idea.