So i'm on version 5.9.8d and I'm not able to craft the Reactor Casing.

http://prntscr.com/kotvdl

Thank you

Is this on a server? If so, if you type into jei @pam does anything show up?

Thank you

Yes I'm playing on a server with a friend and when I type @pam it doesn't show up anything.

http://prntscr.com/kp62pq

In that case, you'll have to manually add the correct version of Pam's to it.
Pam's HarvestCraft 1.12.2u from https://minecraft.curseforge.com/projects/pams-harvestcraft/files.