Advance adapters says it ends up being the same as an older 700R4.
IT SAYS HERE A 700R4 is 23 3/8ths and a 4L60 is 21 3/4
With the adapter it is probably slightly longer than the 23 3/8ths? I never measured but I will next time I am at the garage.
BTW it has run and moved under its own power. Still have lots to do but it is getting there!!