As khubner said, I daresay that's definitely what I've done. I'll have to do a bit more head scratching tomorrow I think. Sorry for the lack of pictures / general disappearance, busy trying to prep the house for the little one due soon.
Many thanks for the advice as well guys, I feel like only I could mess up such a simple job haha.
Edit: I did chop the spacers off, cut off the slider bracket, elongated the rail holes, and then bolted up the rail to this and it certainly doesn't line up. As far as I'm aware the rails are E3 Recaro driver's side as well. Quite puzzling.