transmission

[out back machine]

Hi
my ? is I have a 29 double A that I am putting back together.
it has a new motor installed, new 1930 rear end installed. this is how
I got the truck so now I want to install the tans, and coupler shaft. and the info, I have found says the coupler shaft can not be put in unless the rear end is moved back ? . please don't tell me this is true, how can I get the shaft in place the way its set up now.
thanks for your time