I'm sure it's not impossible to install heat but are you sure you don't want to just buy one with heat...and A/C for that matter? They aren't particularly rare with both. Having said that, I bought an '83 FJ45 Troopy with A/C and no heat but that is a pretty rare vehicle to find in decent condition, the 70 series are way, way more plentiful.
If you are dead set on this particular 70 then I would try to get it installed in the middle east. There are active members on here from both UAE and KSA that could possibly help.