... and 6” with 205 70x15 at the back.
Consideration should be given to your spider gears in the diff. With those extra tall truck tires, a small spare will make the side gears and spiders of your diff spin fast in the diff housing.
My rear tire is 215/60/15s on Fuchs, so a bit shorter than stock. When I went to fit a spare, I used a 155/80/15 and an original 4½ Fuchs since that fits easier in the spare tire slot than a 165. I was pleasantly surprised when I offered the spare up to the rear tire and saw they were exactly the same diameter! This is very important since I have a ZF in the trans. The last thing you want with a LSD is two different rear tire diameters.
I think you should try to find the tallest tire that will fit in the spare slot.