then those are useless shops - they dont know how to work - if you can locate a wide - evaporator with squirrel cage blower assy (old toyota crown rear A/C) - you can easily have a box crafted for the roof middle mount. Or you can have a largish evaporator and flexiducting to little vents (the bus vents I mentioned).
The compressor would have to be a Sanden 8 series or 7 series, but with cut off valve for the suction and supply lines at the evaporator. depending on the system you get your hands on - you may get an orifice tube or a TX valve system (that will define whether you use a drier in the discharge line or an accumulator in the suction line.
The condenser (which should be multiflow) placement should ideally be at the front of the van with its own heavy duty dedicated fans. To help regulate engine temps also. That is why I have mentioned to get a more robust and torquey engine.
As I mentioned you would need to locate a shop that knows how to install complete systems - not a shop that knows how to replace A/C parts - sadly nearly all shops on Tariq Road are parts fitters. btw, there is an old A/C parts shop in the tariq road market - which has a very very good selection of used A/C parts - I bought my VW Golf mk2 roundtube condenser from that place. (That condenser being available in Pakistan is like finding molars in a chicken)