We’re replacing the ugly blue 1970s wall hung toilet in our master bath with an American Standard Glenwall. We got the old one off and the waste horn (cast iron) was sticking out too far according to the new toilet specs - 3/4” instead of 5/16”. Was thinking I would have to build the wall out to compensate until I finally got the old waste horn off (woohoo!). Can I now replace the cast iron waste horn with PVC of the correct diameter? I did a quick online search and didn’t find anything specific for “waste horn”. Thanks in advance for your guidance!