Crash-Roll:

Eight holes across the dash-top flange for the crash-roll studs: (Richard Mills)

Mounting:

Dashboard brackets go over the studs first, then the plates are used to bolt them up to the underside of the dash-top. This from Brendan Hussey, glovebox side, green arrow is the bracket on the dashboard, which was the only way it fitted neatly:

These are mine done over 30 years ago i.e. the same as Brendan - instrument side:

Glovebox side:

After fitting both mine and Brendan's have a narrow gap between the top of the dashboard and the underside of the crash-roll - about 3mm or 1/8", running the full width. It's really only visible if your eye-line is below the level of the crash-roll. It's been convenient for mounting switch illumination on the V8 and supplementary warning lights on the roadster. V8 - quite possibly original with the same beading underneath as on top:

Roadster replaced in 1990, no beading underneath but there is on top (if you can't see it while driving ...):