First time rebuilding 727. got it back together and installed. haven't added fluid yet. doesn't go into reverse or park. what am i missing. ?

if you disconnect the rod down at the trans horizontle shift lever, can you move the lever into the 6 positions?

Don't feel bad. Anytime I worked on an automatic transmission it never moved again under it's own power.

Won't do much of anything without fluid Certainly not reverse

I was thinking of all the internal problems and Robert nailed the most common problem right here.

It may just be a linkage problem. Usually an adjustment.

Make sure the levers on the top of the transmission are not hitting anything or each other.

It it stops short of reverse or park pull the pan and have a look inside.

There are a couple places to look first inside the pan.
The only parts of the valve body that move are the parking pawl rod and this shift valve marked with the red arrow.
It is doubtful you could get the valve body in with the rod out of place because it sticks so far out of the main body and into the tail housing but look for interference. Images here -> https://www.jeepforum.com/forum/f8/tf-999-leaking-shift-kick-down-1207701/

Also there is a detent ball assembly under the parking rod make sure it is correctly moving.