Frame lengthing

Kicking around the idea or taking my 06 crewcab shortbox and lengthing the frame to the longbox wheelbase. id like to achieve a goal of either ending up with a crewcab longbox single wheel or crewcab with 8foot flatbed and duals. I don't want to piece in a small section of fram and end up having two joints per side. My idea is to take and cut the back half of frame off and get straight rails, make cross members and weld up a whole new rear section. I am thinking that would be a lot stronger but also need to keep some flexablity in it....any input is welcome

Just do the pieces. To say you want to not have two splices per side, but to completely fab up the entire rear end sounds crazy. Putting pieces in has been done hundreds of times. If done correctly, you'll have no issues. When $$$ falls from trees, I'm putting a long bed on my truck.

I know it's the wrong brand for you, but it ain't no thing. I'd have already done it if the kit didn't cost $2600.

http://www.longbedmytruck.com/

Split it over the axle. Put on taller front hangers. Move the overload stops. Lengthen drive shaft, brake lines, wires, exhaust. Couple hours. LOL

I did shortbed conversion on a 99 superduty.
And two dodge shortbed conversions. Shop owner ASE master blah blah blah....
I would go to a pick apart junkyard etc and snag a whole rear section from the truck you want. The length is between the axle and cab so it can not be added over the axle easily.
Obtaining the whjole rear frame section should be fairly cheap and almost a direct bolt it weld in affair.

the money you save in fabbing it up yourself if there is any money saved... will be spent in headscratching and problem solving time... causing the truck to sit there sawn in half for long periods of time.

don't worry about having two splices in the frame friend of mine had a mega cab done by long bed my truck... used it for his construction company..never had any trouble with frame strength..

The company's that convert these, cut center of frame above
back tire, on the seam. On boxed frames they have pre made
rail that fits in frame. All they do is weld it.