I'd use ford parts but seince ford used I beams up front I could never get as low as I want.
Get some Dream Beams.
The company that makes them slips my mind ATM, but you can search ebay for "dream beams" and you should find a few there.
Oh and swapping 4x4 to 4x2 will require a transmission from a 4x2 truck. Output shaft is larger on the 4x4 trans, so the shaft in the extension housing wont fit on it.