Here is the process for the flanges between the dash, the A-Pillar and the kickpanel. Wood brackets hot-glued to each piece and the connected together with some scrap sheet metal. Did this for most of the interior panels.
Did this in the car so the brackets are in the exact position.
Then pulled it out of the car and put it back together on saw-horses.
Then laminated the flanges, these will connect the parts together with bolts and rivnuts. Interior guy may modify this but that's above my paygrade.