I have been in sporadic contact with Ute regarding a flatbed for a SB Taco...the bed they recommend for a crew cab tacoma short bed is the 5'8"...still pretty short...guess you could go a little longer but it would overhang a lot...
See the link below for some more Ute pictures within Expedition Portal. I'm building on a Nissan Frontier and Ute bed. Have not started a build thread though.