Also, below is a drawing for an alternate design I've come up with and some photos of others crossmember designs.
I started with a piece of 1/2 x 4 inch flat stock about 48 inches long. The transfer case rubber mount has a large bolt head that protrudes down into the crossmember along with the four holes for the mounting bolts. I drilled these five holes in the flat stock first. I than found that the large bolt head hung down below the 1/2 inch stock, so I added an additional 1/4 inch spacer on top of the new piece.
With the big piece of flat stock bolted up to the rubber mount (transfer case supported with a jack), I began marking for the bends I needed. To complete the bends I would cut part way through the flat stock, bend as needed, and then weld up the cut area.
Once this flat stock crossmember was complete and the eight frame holes drilled, I decided to add some vertical stock to make the crossmember more rigid. I used 1/4 x 1 inch flat stock as shown in attached drawing. I've found this has worked well, with the only drawback being that the crossmember may hold any oil and debris that gets caught in it. There is probably a better way to do it so that this is does not happen so much.
Once the main crossmember was completed, I added a skidplate to protect the transfer case. It is made from 3/16 inch steel plate welded to the crossmember. The photo here shows the added skidplate.
This photo shows the longer skidplate I fabricated after I installed a Marlin dual case setup. I made it longer to cover both cases.
When I lengthened the skidplate I added a second rubber mount to the rear reduction case for added rigidity. I bolted the skidplate onto both mounts shown here.
The reworked crossmember (original skidplate shown here) provides nearly a 2 inch gain in clearance at the transfer case. This makes a considerable difference when trying to drive over obstacles with sharp breakover points, especially when driving a long wheelbase vehicle.
Note the notch in the front of the crossmember for front driveshaft clearance. Also, a 1 inch hole was drilled in the skidplate to accommodate the drain plug. The offset mounting plates on the ends of the crossmember allow me to use the stock frame mount holes yet move the crossmember back about 2 inches. This is because my auto tranny relocates the transfer case 2 inches rearward.
I came up with a simple drawing for another possible t-case crossmember design. This one should be simpler to make but will probably require a tubing bender. I'm not sure about all the fit details. It would probably take building one to fully resolve a final design.
Joe Chacon came up with the nice design seen here. You can find more detail here on his web page.
Joe also came up with a second more elegant design. You can find more detail here on his web page.
This is the crossmember Brian Elliot built for his '85 4Runner.
This is the tubular design crossmember that John James built.
Chris Geiger built this custom crossmember. You can find more detail here on his web page.