At work we have a couple of straight trucks with 24' beds, how far can the load hang off the back? They have been hauling 30' loads and it just looks long to me.
6 feet of overhang? A 30' piece on a 24' bed? In California? No big deal. In your case as long as 2/3 of the total length of the load is supported by the truck bed you're good to go.
You'll need a red flag on the end of the load during daylight hours and red lights if it's being hauled after dark.
If you want to see some long rear overhang check out the guys hauling rebar or power poles on flatbeds.