I have to disagree with the pipe having to be exactly right as we have 2 rig here running modified plastic pipe inserts made from the underground pip we bury for irrigation distric. The one is cut down 18" for H1s and 42s and the other is cut down 21" to fit on home made double beadlocks the work like H1s with 49s on them. Both been over 2-3 years now and no problem.
Myself, my H1s came with the mag inserts so I cut the runflats off and basically made them into 2 piece inserts. They are super easy to install since you can bolt them together in the tire and really light. I also narrowed them up like ¼" to account for the thicker 43 tire bead.