i'm running a CA18 det radiator, which i expect would be the same as the de. my intercooler is 3 inches thick, and sits in the engine bay, behind the radiator support panel. if your cooler is any thinner than a meter, which i would guess it is, you should be able to push it a bit further forward than mine is. i had to machine an unused pulley off the harmonic balancer to fit it. old commodores like that have a two row and a three row copper core, make sure you get a three row, you can tell just by looking at them even if they are in the car. just count the rows. i would reckon they would fit, a 1200 has a lot of room between the headlights. a radiator shop recommended on of these to me.

good luck!