By far, the Xhifhut Body and Bow are the hardest to get. I personally farmed for these last two items for 2 years (no joke... man I wish I was joking). They are hard to get because they are such very rare drops.
First got the Head and Strings while EXPing and helping people out farming testimonies. Way back when I first got a Xhifhut item I was planning on using the mantle for my MNK (+5 Attack was about the best you could get at that level at that time without spending a huge amount of money). By the time I finally got the drop, I'd already taken a couple more jobs to 75, and have much better items :-P
The Bow drops from the PLD Ants in Western Altepa in the area around E-6 to G-5. Took me about 6 months of farming weekly to get that damned drop.
There are Lanistas around these PLD ants, however, after a year of farming those semi-weekly, I never got the body to drop. Not once. So don't even try it.
I also tried farming Signifiers in the caves all over the place. Again, no drop. Finally went to cave entrance at J-9 in Western Altepa and fought the Sigs in there. After many hours, we finally got it to drop.
In other words, take it from me and don't waste your time farming Lanistas... at all. I'm reasonably convinced they don't really drop this damned thing. And, if they do, the only ones that drop it are in some obscure part of the desert that is impractical to get to.
Instead, focus on the Sigs in the cave zone from J-9. Specifically, you want the map where you spawn the NM "Tribunus VII-I". Go in there and kill all the Sigs you can find. Eventually, it will drop.