The thought crossed my mind, but I don't think I can get a set of hubs for free, like the transfer case
A new conversion kit is $1000 in the US, which means around $1300 after shipping and tax here.
This fill-up will have some mixed driving: 231 miles with the street tires, so far and 116 miles with the off-road tires, including mountain trails and fooling around to test the new locking differentials. Previous data shows 20.4 MPG average with the off-road tires so I could take a stab at estimating my street tires real average consumption.