Cast iron soil pipe on concrete floor.

I'm installing a toilet on a concrete slab floor. The rough-in is a straight cast iron 4" pipe that sticks up about 1 1/2", I'm putting in ceramic tile on the concrete. The question is what to do about the flange. I've seen the PVC-types that slide inside the pipe and then you tighten some screws to seal w/ a rubber gasket. But I'm wondering if I need one of them.
My questions are. 1) How can I cut the cast iron down so it will be level w/ the finished floor? I've used a pipe snapper as low as it could go but that only gets it to about 1 1/2"
2) Can I use just some type of ring (that the toilet bolts will stick out of) and screw it to the concrete floor and set the wax ring/toilet right on to the straight cast iron pipe?
Note the concrete is firmly/tightly all around the circumference of the cast iron pipe so no flange like this would seem to work.
This house is from the 50's and it seems like this rough-in would have been common, but I've not done it before.

I'm not sure why the toilet drain was roughed in like that. You may be able to cut it flush with the floor with a grinder or a sawzall then install the type of cast iron closet flange that is inserted into the 4" pipe. It will have bolts that get tightened from the top and it will expand/compress inside the cast iron to make a water tight seal. The closet flange should be anchored properly to the floor when it's installed.

Cast iron soil pipe on concrete floor w/ super ring

I still wonder if I need a flange? Could I attach something to the cement floor and then the wax ring will just seal against the straight cast iron pipe? The toilet will bolt onto this Super Ring.
And any other suggestion for getting the pipe down to floor level? As I've said the pipe snapper only allows you to get so far (a little more than an inch) and if I put a flange on top of that I'm up way too high.

Air Smells

The grinder and sawsall methods to cut the cast are the best. Trying to snap a small piece off the end can crack the pipe. Some use a crescent wrench to snap off the extra piping in pieces but don't crack the pipe if you try this method. The flange idea is suspect. Even if you seal against water you need the flange to seal against the pipe or you will get odors that some to not like.

flange

Why wouldn't you get a cast iron flange and chisel out the cement around the pipe. And when you can sit the new flange on the stub, and it sits flat on the floor, get some lead and oakum and pour a lead joint. Cork it tight then take a small hammer and slowly break off the excess pipe. cork it again. use your bolts and ring and its done. don't forget to shim and grout. Grout is better than calking........