Another Holden in the Family :)

[Micks]

One more stupid question, do you still use an alignment tool if replacing the plate and seal as one, or is it only used when doing just the seal?

Rod no you don't but as explained, doing it that way is hit & miss. I know it can be done though not recommended. Too much work to pull the box again only to do it all again should it leak.
When I did it bought a plate with the seal, removed the seal & binned it, installed alignment tool torqued bolts as per procedure. Good luck with it.