I want to put 10"x15" wheels on my Disco 1, can someone please tell me what offset I need to get, is it -25mm? Thanks Landy chums...

I have a 3.9 V8 Disco 1 auto, I am contemplating whether to put in an American Ford V8 with 400hp & 425ft/lbs of torque, can anyone tell me how much power can the standard auto box and transfer box take??? Thanks fellow "Randy Lovers" Craig in South Africa