I've finally completed fitting the body shell onto the car.
In the top photo it shows where I applied the white coloured bonding paste onto the frame in key points where the shell rests on it. (This was done at the rear too)
The red straps are ratchet straps that I used to hold the body tight up against the frame in the correct place. This proved to be a highly effective solution.
I then put some foam down the sides of the shell at the front edges and fibre glassed the sides of the bulkhead across onto the body.
On the inside I've glassed the front edges of the floor onto the metal floor, and all the way along the sides from the floor up onto the sides of the body.
In all cases I've used two layers of fibre glass on 90 degree angles