Since there isn't much out there anymore with respect to fitting a mk3 instrument cluster into a mk2 dashboard prettily (with the exception of a description and photos provided by GTITDI), I present to you... fitting a mk3 instrument cluster into a mk2 dashboard prettily.
I cut out the mk2 dash back board to fit the width and depth of the mk3 cluster.
I took the existing mk2 cluster bracket that sits closest to the drivers door and cut it at its thinnest point to create 2 new brackets.
I sliced off the parts of the brackets that curve 90 degrees so the metal that was to be riveted to the mk3 plastic cluster mount was flat. I also bent the mounting tabs on the ends of the bracket to fit the contours of the mk2 dash back board.
This is the part of the dash that is closest to the drivers door, the dash is upside down in this photo.
Both brackets were pop riveted into place. I riveted the leftmost bracket at the diagonal section for more strength.
The biggest pain was trying to figure out where to rivet the plastic mk3 cluster holder to the metal, I knew I wanted the cluster to sit so it doesnt exactly touch the dashboard at the top so it is easier to get in and out once the dash is back in the car.
Next challenge is modifying the mk2 bezel plastic to accommodate for the mk3 cluster. I took a mk3 bezel and trimmed it to fit the mk2 bezel. I had to cut and heat and mold the mk2 bezel to accommodate the mk3 plastic.
Bottom of the mk3 bezel needs to be that thick in order to touch the mk3 cluster.
I widened the mk2 cluster plastic to 208mm at it's widest point near the bottom.
I will use a harbor freight 80w plastic welder and noryl rod to fuse the two bezels together.
https://www.mcmaster.com/noryl-rods