Old Shower Base Drain with no visible flange?

[NativeNYerChicHK]

I am about to embark on a full bathroom remodel and have a doozy of a problem that has me quite baffled... It currently has a stand up shower but with a molded shower base pan that I will be changing out for a tiled shower floor. And I believe what’s there now may be original to he home, built in 1982.
I am still investigating what I’ve got and educating myself on how to properly remove the old to replace with the new.

So I took the screwless snap-on cover to the shower drain off to see what type of drain assembly was used, normally it’s some type of a compression fitting in these things. But what I found was nothing I can make sense of. What’s there is the edge of the shower base, then mortar and then the center PVC drain pipe, that’s it. Whoever built this shower did not use the cap that the snap on drain cover is supposed to fit into, they made their own with mortar. The only thing I can imagine is that they must have depressed the snap on cover into wet mortar, removed it to let it dry and just used that mold to hold the drain cover in place. It is not siliconed either, it just sits into the man-made groves in the mortar underneath it. This is on my second floor of my home, not a concrete slab. I really don’t want to have to open the ceiling of my living room, we’ve already had to open it and patch the ceiling for a leak, thus the reason for this remodel. It wasn’t the drain that leaked though, it was grout failure that we were able to patch temporarily which bought us a little more time in order to be able to do this remodel right, not under duress.
I’m thinking there must be a compression ring under that mortar but I can’t be sure until I start taking this out. Attached pic is what I’m talking about.
What I think I’m going to have to do it cut the shower base around the drain, detach it from the studs and remove the majority of the base. Then I think I will be able to have a better look at what was used to secure this drain pipe into this base without it ever leaking. I am hoping to see something I recognize so that I will be able to remove it all without damaging the drainpipe or having to cut it back too far. I can do minor plumbing like replacing a drain assembly which I was hoping to be able to do here myself and not have to spend the money on a plumber to figure out this mess.
So has anyone seen a drain encased in mortar like this in a shower with a moulded base?
I have been searching online plumbing blogs, online forums and YouTube videos and cannot find one mention of anyone running into this type of drain set up. I’m thinking there is a compression ring under this mortar, or at least I’m hoping that’s the case. If it is, that can easily be carefully drilled out, the compression ring removed and that will free up the drain pipe for use with my new drain assembly.
Please tell me someone has seen this before and has some good advice for me, I’m really at my wits end on how to proceed until I can start the demo a few weeks from now. I like to be educate myself to be as prepared as I can be, I don’t like surprises - especially costly ones, and I can’t find anything that even remotely looks like this.
If I do have to cut the drain pipe down to remove this mess then I know I could use a coupler and a new riser but I really don’t want to have to do that. I know it meets code but by my own estimation, the less interference (cuts and reattachments) in piping, the less of a chance of leaks from any extra fittings or failures at glued together pieces.

Help! Please?

 

[OLD TIMER]

It's a hack job. unless your removing the shower floor I wouldn't touch it.

 

[Sponsor]

 

[Orangewood]

If you're pulling out that base anyway, just take a sawzall to it.

 

[hj]

In most cases the drain line is already too high for a tiled shower drain, but all you have to do at this stage is just cut the drain fitting apart without damaging the riser, which should be no problem.

 

[NativeNYerChicHK]

HJ, oh how I do hope it’ll be that easy. I keep looking at it thinking it should be that easy, its definitely far too high as is for the Kerdi drain so I knew I’d be cutting it somewhat. I just feel like there’s just no way it’s going to be that easy, it’s the Irish in me, Murphy’s law applies to everything in my life
I’ve never seen a drain missing the ring that the drain cover is supposed to fit into like this, it really looks unprofessional. That’s why I asked here, hoping that maybe somebody had seen this before and could give me a different perspective about handling it that I hadn’t already considered. I do believe this is the original shower to the home, I honestly think the prior homeowners only ever wallpapered in there, of course over other layers of wallpaper, those lovely people... They were awful DIYers that did a heck of a lot of things terribly wrong in this house so thats really what’s got me worried about what might be under there. Maybe they did do this hack job and some awful surprise is waiting for me as soon as I lift this base.
But as it stands now, my only real option is to sawzall the base around this drain and remove the it to reveal how deep that mortar or old hardened putty goes down around this pipe. Hoping to see at least a part of a recognizable drain assembly on the underside, at the very least. It’s got to be there, it’s just got to. This drain has never leaked, something besides mortar or old hardened putty is keeping the water flowing into that pipe.
I’ll update as soon as I get to starting.