[opelbits]

Humm I'll be darned I did not know that.
How weird is that they couldn't have had a better plan

The GT was not designed for a/c. That is for GM compressor, which is a long cylinder shape. An R6, I think. There was no where else to fit it in the engine bay. The other system, the ARA, used a compressor more like the square Ford York or Tecumseh and it was small enough to mount over next to the thermostat housing.
Other signs of a GM compressor are the alternate locations for the coil and washer bottle.
With the condenser in place in front of the radiator, I am inclined to believe, but am probably wrong, that they used a smaller battery to fit down in there.
Has anyone seen evidence of a rotated battery/tray that keeps the battery away from the condensor?

 

[opelbits]

Not sure it would leak oil out....both valve cover hoses help create a vacuum in the cover, so maybe it would reduce the effectiveness of that by drawing air in?