Care and patience!
Factory tool is help full bu not essential.
The method I use is to line up the plates as best as is possible using a straight edge steel ruler. Then put in two springs/bolts opposite each other and do up part way allowing the plates to move a little but not loose and floppy. Gently tap the drum on, withdrawing and realigning plates as necessary until you can tap it all the way home. Then very carefully withdraw and tighten up the bolts a bit more, hopefully the drum will slide back on again easily, if so insert and tighten all the other springs and bolts.
I don't know the torque figure, I have simply done them up reasonably tight using a 1/4" drive 10mm socket and a spot of Loctite.
James