for the skyline box - there is minimal tunnel mods that need to be made.

mainly due to the size of the transfer box, Martoon has belhousing mods that pretty much allow it to fit up with not alot of agro.

Barra box is what id buy, for the money its possibly a good route to take, but is restricted on the size of what can fit inside the gearbox casing.

same issues will occur with the fixit, but downside with fixit is it can take anything up to a year to get it fixed if anything breakes on it - the back up support is purely shocking!!