Tubes are self checking if leg assemblies are out of the tree. Put tube against tube, turn 90 degrees and check, repeat, ..but new ones should be good.
If your lower tree is bent. Grab stem in vise with wooden pads. Then slip your old tubes in, clamp, and start bending.. Use a snipe if need be. Then use new tubes to check..
It will be quite bendy.....
Its strength is in the whole assembly bolted together with both trees in place.