Here is a splitter I made for my larger top mount intercooler:

I made it from a sheet of metal from lowes, I think it was either 16gauge or 18 guage sheet metal. Also to bend the pieces, i made a quick sheet metal brake. And to make the holes, i found a socket that fit inside of another socket and just drilled a hole and set up the sockets and hammered them together to make a dimpled hole.