Inline 4 adventure bike, tyre recommendations?

[Woodman]

I got a half worn/melted 120/90/17 here if you want to try it. As long as you don't give it back its yours for free. Its only done one Molesworth/Rainbow loop on the back of the KLR.

[Gremlin]

TKC80's 180/55-17 for the rear and 120/90-17 for the front?

figure 120/90 as opposed to 120/70,, gain a little bit in diameter?

I'd stay stock. Unless you're modifying the bike, you might end up with clearance issues. With the TKC80, the knobs are about the same size as regular tyres, ie, the base of the rubber has a smaller circumference than a regular road tyre (because the gaps between blocks are deeper than grooves).

TKC80 fits the CB900 fine, no problems with swingarm/mudguard clearances.

The reason you're struggling for tyre size is that dual purpose bikes simply don't have a 120/70/17 and 180/55/17 profile. About the most road biased dual purpose gets is 110/80/19 and 150/70/17. Everything else goes more off road biased (21/18 combos and smaller)