There used to be a place here on Broadway that had one about that size hanging in a tree. They had a padded chain wrapped around one of the branches it hung from. The chain hung loosely around the branch so plenty of room for it to grow. The top was padded with a thick rubber, probably a tire truck. It was a huge old oak so the weight didn't seem to be a problem. Good luck with it.
Tally HO!

Our Staghorn weighs several hundred pounds and is about 15 feet or more in circumference. Several years ago, after the plant had grown alot, we rehung it on our wood patio cover,putting chain through clear plastic tubing and made a 4 chain cradle for the plant, setting the plant in the cradle and attached the chains together above the top of the fern and then ran the chain over a 4" x 4" wood patio runner that came out from the house and rested on another long perpendicular runner. To make a long story short, the patio roof rested on pylons and the side the staghorn was on dipped severely after winter rains, with all the weight of the staghorn on the pylon and it sinking into the wet earth. We had to get it down with an engine puller. My son had to make a rolling cart to lower it into and then he set the engine puller over the runner and attached it to the chain and gently lowered it.

It will sit forever in it's new cradle.

Moral of this story, make certain that Oak limb will hold the staghorn because it will continue to grow and don't stand under the old Oak Tree!