Re: Three piece bed
If your springs are set right it shouldn't matter. I think the one piece is usually in the walk through layouts, whereas the later 50s have the 1/3, 2/3 split. The SMB style is just small cleats and a cable loop, the latter is available at any hardware store not sure about the cleats. I think I've seen a L-shaped strap that is fastened on the bottom of the bed in a DIY post somewhere.
Incidentially when I want to get rid of the rear 1/3 I just turn it up so it sits on end and leans on the back of the PH canvas. If you do that with all 3 you'll only be taking up about 12".