Ok I've got a idea that's been brewing in my head,on the Montana and the grand prixs the headlight control is the same,the window plugs are the same,a lot of plugs under the hood,time wouldn't be a problem,I want to do the 3.8 sc motor in a Montana but I'm thinking of the wiring harness took of the gp and taking the Montana's harness out of the dash and putting a gp one in,the only issue I think would be rear air and windows and the DVD player and dic if I got a Montana with those 2 options,the speedo dosent seem it'd be hard and radio,the Montana would have to be 00 and down to use the same radio,I 100% know the window switches cross reference cause in the montana I had the the switch was bad and I took it out of the gp and temporarily put it in the Montana and the ac heat blower wouldn't be hard and manual ac controls shouldn't be hard and tailights should be a problem,what do you guys think,with time I think this would work