Why does everything go back to your rodeo? Didn't we go thru this before.....I was about to ask this same questions. I'm currently stock 4x4 nismo and would like the same input on this. I want more up/down wheel travel, i hate how tight this thing feels on the whoops, shakes me and the passengers around a lot at lower speeds on the whoopy roads unlike my rodeo, on the rodeo I just cranked the torsion bars so it sits 3" higher in front and installed longer shocks, WOW, BIG difference, feels incredddible vs. stock height&shocks, sometimes wish this frontier sat on torsions, cheap, easy, very beneficial, reliable mod.
Now for the OP, I would try your 2.5" Icons first and see if they work. You may have to crank them a little or add a small spacer but they should work. Now if this doesn't work, then I would figure out the full compressed and full extended length and order a CO that meets those specs. I am sure PRG will have an answer if you can get ahold of him.