Lay plates up to side of tunnel and find index hole to position plates. (See photo)
Drill out all existing pop rivets that would interfere under the new plate. Do not drill out the solid rivets in drop bracket or tunnel, just the pop rivets.
After locating the indexing hole for the right position of the plates, start with this hole and install rivet. Make sure plates are snug to the top of the tunnel. (See photo)
Finish drilling out all holes through tunnel using holes in tunnel plate for a pilot hole.
If there are any pop rivet holes in the factory tunnel that were covered by the new plate, then drill from the inside of the tunnel through new plate and install rivets.
Use longer rivets on all the upper holes and the shorter ones on the lower holes; install the short ones from the inside out for track clearance.
There is one rivet that was drilled out in the center of the tunnel through the drop bracket, finish drilling from inside through new tunnel brace and install rivet.