If you want to leave the floor in tact (at least for now) see if you can access this plumbing from a blowout in the ceiling of the room below.
Either way you should definitely replace the lead with PVC. This can be very tricky because the old lead bends can be molded into whatever angle, offset, length and hight protruding through the floor upstairs where the toilet sits. With PVC you only have increments to work with (Ells, street ells, 45's, street 45's, 22 and street 22's, etc.) Each of these fittings also have "vent" counterparts (vent ell, vent street ell, etc.) Vent fittings are "shorter turn" versions of these fittings. You may have to make some ridiculously awesome super fitting out of 2-3 of these individual fittings to match your old lead's bend. And then, you have to contend with the fact that if you pull the floor and put down a new one, there may not be enough room above your final pvc pipe hub to accomodate the female toilet flange's hub under the floor. Or vise versa if you try to leave the final hub at the correct hight to glue in a street flange, there may be too much room and your flange wont reach the hub. AND THEN you may have to change the distance off the back wall. Most modern toilets require 12" from the tank wall to center of the toilet flange. Some older toilets used 11" or even 10" stand-off from the tank wall (like maybe that old AS you pulled).
Basically what im trying to say is when my boss tells me at 4:30pm to go change a lead bend, I cry a little on the inside. If you can find a plumber worth his salt have him do it. Changing lead bends to PVC is a real pain in the d**k if she's a tight bend. This is where most DIY'ers get themselves unto trouble because 3 hours in they settle for "good enough" instead of "correct".
BUUUT if you can get us some pictures (preferably with a tape measure so we can see how tight we need to work) it's do-able.
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