Telescoping Closet Flange

The toilet drain I'm tiling near has a telescoping PVC closet flange placed over an old cast iron flange. It has 3 allen head bolts and nuts that can be adjusted to raise and lower the flange. It also has a rubber gasket that seals it against the old cast iron pipe. I unscrewed the flange and removed it, so I can add cement board and tile.

I'm worried that adjusted to the highest position, it may still be too short to sit on top of a newly tiled floor and still maintain a tight seal with the rubber gasket inside the cast iron flange.

Do they make longer telescoping flanges that can sit inside an old cast iron flange? Or is there another way of sealing this one better?

Does anyone have any ideas about how to add a flange to a disintegrated old cast iron flange to raise it up about 4 inches and maintain a good seal. Or does the old flange have to come out? Keep in mind that there is no access under the bathroom.

The retired plumber, who last worked on this toilet, put in the aforementioned telescoping flange. But, he made other mistakes, so I don't really trust anything he did.

I would buy a deep cast iron closet flange and remove the old one...
I would lead and oakum the new one on the old pipe (after tiling...)...

Is it possible (for a plumber, not me) to lead and oakum the new flange on the old pipe with the old flange still there? The top of the old flange is currently buried under plywood, cement board, and tiles. The pipe is accessible, and its i.d. is about 4".

Another source said I could use a deep 3" PVC flange (see picture) and attach a no hub coupling to the bottom. and the rubber should seal it to the CI pipe once the flange is anchored into the floor. Is that okay?

This is what the retired plumber was using, but even with the rubber ring at the bottom, it doesn't seal against the inner part of the CI pipe.

The older the CI, the harder it is to get a good seal in that manner...corrosion, deposits, etc. make it less than smooth.

Leading in a new one seems like it would be best, but if you can find it, there is an alternate product that meets code. Basically, you tamp in oakum, then put a layer of this sealant, then repeat so you have three layers of oakum and sealant. Finding the stuff may be the hard part.

Turns out the retired plumber did have the right flange. I was just using it wrong. It's not a telescoping flange at all. You have to loosen the allen screws, place it over the CI pipe and then tighten up the allen screws. This actually shortens the length, but it flares out the rubber seal. Got a nice tight seal before screwing it into the tile.

BTW, the glass and tile bit I bought sucks. It's one of the little pointy spade ones and I had to work like hell to drill a few small holes in the tile.

Is there a better tile bit out there? My masonary bits wouldn't even prick these tiles either.