I did 2 ways.
1st was to wedge the sound board onto the neck.
But the assembly and binding is a hard to do.
2nd way is my current way.
I build the heel and neck separately.
Heel onto top like normal Spanish guitar assembly
Finally after everything done (including binding) then the neck is attach.
I use some dowels to align the neck top and heel
Can see more of the sequence in detail on my #3