Account bound versions of this gear would be great.
An appropriate monster for Vali's Manteaus would be Removers I think. They are not bad monsters to hunt exp wise as long as you're nontrans, and with a small party (2~3) they should be manageable at Level 60~70, where you really start needing the extra reduction that an immune provides. Plus, being undead, even FS priests can solo them if they are desperate, giving them a chance to gear up for the harder levelling that's coming up.
Falcon Mufflers are a bit tougher, since characters that need flee will probably need it a lot sooner than characters that need neutral reduction. That being said, the pantie/undershirt combo already exists, so it isn't absolutely necessary to put a lot of weight on this item. Making it come from somewhere like...Rachel Sanctuary 1 (Vanberks and Isillas), where you have low dex monsters, so flee characters will be more prone to level there. Again, the dungeon is manageable at 60~70 with a duo (I used to solo there on a 6x Assassin as well), so it's just around that time where a players gear really determines where they can level.
Vidars Boots are more of a luxury gear than the other two. While flee characters will decide their levelling spots based on their flee, and others will have a huge increase in survivability with neutral reduction, the HP/SP of Vidar's Boots does little other than reduce downtime. That means you can afford to put them on a bit higher level monsters than otherwise. Wooden Golems might be a good spot for that, the exp isn't fantastic but it makes them go off the beaten path a bit to get the proper gear. Alternatively, something like Alarms or Mermen could also be reasonable spots.
If I had complete and total freedom, I would probably make something like Overlook again, where the farther down in the dungeon you go, the more gear you get. So on the first level of the dungeon, you'd get a turn in quest that gives you a choice of Vali's Manteau or Falcon Muffler (bound). The second level, maybe 5~10 levels higher than the first, gives you a choice of Green Shoes or Blue Shoes (10% MHP/HPregen for green, 10%MSP/SPregen for blue). The third level, another 5~10 levels higher, would give you the choice of a bound shield (10% reduc from all races) or a bound armor (+5 ATK, +2% MATK). The last level would reward you with a choice of any card from the dungeon, like Overlook does. I'd probably start the dungeon aimed at about level 45~50, and try and end it at about 75~80.
IMHO