Update!
Changed the core plugs, one took a few times to seal properly. But (touch-wood), they seem to have sealed up nicely!
I've got my gawgeous front seats fitted too!
I've been Pm'd a few times about how they fit and the frames I have made, so here goes my explanation...
I welded a beam to the front of the runners at 90 degrees, this way there was a bar running the full length of the cross-member.
To support the rears I welded a small piece of box section to the outer runner and another to the inner runner. However, due to the exhaust tunnel, the inner box section was modified to create a triangular piece to fit round the tunnel. I then ran a bar between these box sections for additional support.

To secure them, I used 3 tech-screws drilled straight into the cross-member and another drilled through the floor into the beam joining the outer and inner box sections.

I'll upload the pics of the fronts later.
Much love,
T.