Purchase the cross member from summit, it will be perfect. Exhaust may get in the way, mine did. You will need flex plate, shifter cable and have to shorten the drive shaft. You can use a first gen. shifter and a conversion kit to adapt to the 4 speed auto trans. You will also need the electrical plug on the drivers side of the trans and another brake switch in the second position above the brake pedals, this will be wired in to unlock the converter. A b&m kit for converter lock up.
You may want to consider a 200r4. A 200r4 will be an easier fit. The bell housing is a direct bolt on, the drive line will work as is & the bell housing is smaller & will fit into the trans tunnel a little easier. Just a thought.
Just to be clear, a 700-R4 will NOT bolt up to a Pontiac engine. Not without an adapter kit. It's a Chevy only bolt pattern unlike to 200-4R which will bolt up directly.