As I wrote you in response to the PM you sent me:
"Yes, changing the final drive affect all gears. However, I'm not sure where you are planning on getting a 3.88 final drive. If you are driving IMA-less I would consider an HCH Swap, which will get you a 12.2% lower 3.6 Final drive."
Are you looking at the 3.842 final drive that was used in the 7th gen Civic HX? If that's the case, it's important to understand that the 7th gen Civic HX came equip with a "D" series engine. Honda's D series engine spins in the opposite direction as compared to the Insight's engine as well as the "L" series engines used in the HCH and Fit.
While it's more than likely that the ring and pinion would physically fit, the helical gears are cut in the opposite direction and that is going to alter the thrust loads on the bearings inside the transmission in a way Honda never intended. Without further analysis, it's hard to say what the repercussions of that would be.
Non-sequitur: I need to update my HCH Transmission Swap Anthology thread with a nice comparison graph like the one I did in this thread.
Oh of course that's right, some Hondas have the engine on the left instead of the right like the Insight, and so of course the gears would be different with an engine turning the other direction! Oops!