Heres a thought on how to get that droopy one up just a bit, before you lock it in place with that Y bracing.
You might haveone of those hydraulic car jacks (they're pretty cheap and they can lift, like 2000 or more pounds...
anyways... put it on some scrap wood on the ground, and then put a 2x4 or 4x4 on it, wedged up against the bottom of your "droopster" (all the way out at the far end for the best leverage...
Then "jack the bejeebers outta it" til its level.
Then nail in the Y brace so's everythings under tension...
You don't want it not level, because depending on how far out of level it is, your wheel(s) on that side/end might have the potential to come up/off the track... that would be BAD.
It doesn't have to be perfectly level, though, but just jack it and tack it as close as possible.