What you have linked to is not really a truss, it's a brace. Your comment about it being "beefy' is a giveaway. Trusses are designed to be strong and light by proper placement of minimal size material.
Not exactly. No matter whether the truss is above or below, some members are in tension while other members are in compression. That's what makes a truss design work.
So why do you think you need a truss anyway. That pumpkin in the center looks big but it's not that heavy so it doesn't need a lot of support. The weight of the Jeep is supported pretty near the ends of the axles and near the tires so unless you are carrying a lot of weight and/or doing Evel Knievel style jumps or land really hard coming off of a boulder, you probably don't need much.
Well, there is one other consideration, torque. With an NV4500 and a Tera-Low or Atlas case, you would have a gear ratio of 25:1 multiplying the engine torque into the differential trying to twist it about the pinion axis. Drag racers used to have a strange looking brace for this that was heavy on the top of the axle on one side and on the bottom on the other side but until they started doing the burnouts, they never backed up.
Now for the design, first, it's not easy to weld to cast so to avoid that, assuming a rear cover diff., I'd cut and drill a plate to fit under the cover. This would also add strength to the case. The plate would have tabs bent over at the top and bottom to weld to the truss members. Also note that the one you linked to has coils. If your application doesn't, you need to end the truss before the U-bolts or do something special to accommodate them.
Here's a design I came up with a few years ago. I never built it so it's untested.