Niall, no need to re-edit, just deliver SD since everything is SD.
Create a new sequence in FC, drop one of your 2997 stock footage clips into the timeline and say yes to match settings. Delete that clip from the timeline.
Copy everything from your current “HD 23.98” sequence and paste it into your new SD sequence.
Select everything in your new SD sequence and right click>remove attributes>position and distort. Everything should look good and you shouldn’t have to render anything (unless you have effects).
Now just export that straight as is, SD 2997. An HD 23.98 delivery will a nightmare with QC.