Toilet flange/Sub-floor

I'm remodeling my 1950's bathroom and have a question about my old (cast iron?) toilet flange - photos below.

I'm ready to put down my sub-floor, but just noticed there are no bolt holes in my flange - maybe they're rusted over, but I've scraped and poked and can't find any evidence of holes there.

Do I need to replace the flange, and if so, what do I replace it with - PVC? ABS? What kind of adapter? Cut the pipe at the vertical or horizontal?

Thanks in advance,

Greg

EDIT: OK, looks like this flange is going to be too low (beefing up floor), so I definitely a replacement/extension option. Anyone have experience with these kind of replacement flanges (third photo)? Looks like I drop it into the cast iron pipe, tighten the allen screws to expand inside the pipe and adjust height.

EDIT 2: Can anyone verify the solution I was given? Someone told me to cut the cast iron (using a chain cutter) 4-6 inches past the elbow, then replace with PVC, including a new PVC flange. Good solution?

EDIT 3: Guess this is a boring topic. Maybe I should have put "pex" in the subject line. =)