To set the stage...

I just installed a ceramic tile floor in the bathroom and needed to raise my existing cast iron closet flange. The flange was leaded to the waste pipe. I peeled the lead away from the flange to free it up and raised the flange 3/4" or so with blocking. I tapped the lead back in place with a hammer and see that due to the increased flange height, the lead is now short in a couple of spots, and doesn't seal up all the way around.

Anyway, I bought an Oatey PVC to cast replacement flange. Should I peel and remove the entire lead sleeve, creating a clean pipe prior to installing the replacement flange? Or can I simply leave the lead in place and install the new flange?

Thanks for any help.