WHen using the T-slots, you want the small end of the slot on either side to be at the flange rough-in distance, or maybe with a slight amount of room to the end of that slot. This is the strongest part of the slot. The SS ring is good. The flange you have has a socket on the bottom. This means you need to measure carefully to get the riser length proper so the pipe gets seated, and isn't too long or too short. They do make a similar flange that is more like a coupling...the pipe can be left long, the flange slid over it, then the pipe is cut off flush with the top of the flange when you're done. What you have will work fine, but measure carefully (you cannot dry fit, as the pipe won't bottom in the sockets until it melts with the cement). The Carlyle typically has about 3/4" clearance behind it when the rough-in is exact. There's more room at the base, so you shouldn't worry about a typical baseboard...only if it were very thick. When you install the Unifit adapter, you can fudge it forward maybe 1/4" or so from being exactly centered on the flange if you need it, but you probably won't. You do not want to be applying stress to the drain pipe. If you can't make it work, you may need to redo the pipe.