I don't think there is another way to do this properly.
To get this right I'll first have to take of the roof off and then the back panel .
The bolts/screws are somewhat rusty so that might be tricky

getting the rusted nails out of the wood is hard enough
I guess only time will tell and with a lot of patience and the right tools this should be OK.
My intention is to do the floor bit first and than put the body on a frame.
Take the roof and back panel of and clean all the wood , check all the joints ect. ect.
reassemble the body and putting it back on the chassis for final alinement's .
Than doing the fabric !!!
The body work is not a first for me but the fabric is so that will be a nice challenge to get right

Regards,
Halbe