my dad did some research and the new motor is out of a front wheel drive vehicle chances are then compression ratio will be 10:1 , the stock montero 3.0 is according to his research 8.5:1, im hoping this is all true.
as far as the turbo on a sohc mitsubishi never made one from the factory, i think there are kits for a turbo to be put on the sohc, the (t) that the guys put on valve cover is my guess to what they were doing