After the base frame was completed, I made tabs that fit the gas tank mounting locations and tack welded them to the battery rack. Then I made the upper frame of the battery rack.
The left mounting tab is in place and ready to be tack welded.
The right mounting tab is at a compound angle and many cuts must be made to fit the many curves of the car's frame.
The frame is complete. The right, front corner of the upper frame bolts into place and is designed to clamp the batteries securely in place.
Here is the rack populated with 28 cells. There will be a sheet metal base to support the cells, and open sides, as the cells in the trunk are fully protected from road splash. The top will be covered with an acrylic sheet to protect against voltage hazard, but still keep the cells visible - especially important if the car is ever displayed.