Seat belt top anchor point/tower

Hi all,
my Mx5 (91 Vspec) has (well, had now) an after market roll bar fitted
(not a stylebar, this thing is steel, braced and heavy), basically it
was fitted ot the seat belt towers, and braced to the a bracket mounted
on the parcel deck, it was fitted by the previous owner, years before I
bought the car, and that was about 3 years ago.

Anyway, took it for a warrant of fitness today and it fails, because
the seatbelt top anchor was bolted through the rollbar bracket (ie part
of the rollbar bracket is sandwiched between the top of the seat belt
tower, and the seat belt bracket), and this apparently requires
certification as it consitutes a "structural modification".

The guy doing the warrant told me to take the bar off, come back and
get the warrant, then put the bar back on again (and next time, make
sure the hood is up when taking it for a warrant so nobody will think
to check it).

To cut a long story short, I need somebody who knows how this top
portion of the seatbelt is assembled from the factory, because I'm
pretty sure I've got a missing part. I've taken some pictures...

First one:

http://host.gogo.co.nz/100_0301.JPG

This shows the top of the seat belt tower, the rollbar base basically
sat on top of that and was also bolted to the back of the tower -
leaving the gap underneath, and the top of the seat belt bolted through
it, with two spacers sitting between it and the bracket to raise it up
to the correct height.

Second one:

http://host.gogo.co.nz/100_0302.JPG

I had in the boot a couple more spacers which seem like they must have
been from the original seat belt assembly. They fit nicely in the
hollow with the top of the spacer level with the top of the tower.

Third one:

http://host.gogo.co.nz/100_0303.JPG

But if I were to just sit the two spacers that were atop of the rollbar
bracket (to bring the top of the seat belt to the correct height), that
just looks really dodgy, like going to bend at the first sign of
stopping in a hurry dodgy.

I think that what I'm missing is a plate that must sit atop that tower,
with the large spacer underneath it, and the two small ones on top.

Can anybody confirm this before I go get a couple cut?