I would definitely pull the crossmember. Since the motor's already out, it's not even a question in my mind.
I did this on my '68 Chevy 3/4T last summer with the motor in place. Note the wooden beam and strap arrangement holding up the front end of the motor.
http://67-72chevytrucks.com/vboard/s...d.php?t=587600
Set the truck up pretty high on jack stands that are just forward of the firewall. (you want the bumper far enough up in the air to clear everything you're going to roll out later) IIRC, there are 16 bolts to remove, but two of those tie the motor mounts to the crossmember. I would think that you could leave those in place. That leaves four sets of three bolts between the frame and the crossmember, plus the steering, drag link, and brakes to cut loose.
All the fasteners that had to come out from the bottom came out first. Just plan so that the last six bolts that you take out are the horizontal ones tying the x-member to the frame. A second set of jack stands would be good as you're dropping the x-member onto the floor jack, but not necessary. I just made sure that I wasn't doing anything except reaching in through the wheel well.
The lower ball joints will need encouragement coming out and going in both. With the crossmember out of the vehicle, it's easy to remove the a-arm and use an arbor press for this. The arbor press at your local shop is a much better tool than the on-car kit that you borrow from O'Reilly's. Uppers will be a matter of cutting the rivets and bolting the new ones in.
I used all Moog wear items from RockAuto.