How do you fit a scimitar se5 axle on to a vauxhall viva?

I have a 1973 Vauxhall Viva and have put a Rover 3.5 V8 engine in it. The origonal diff will not cope with the power or torque of this engine. I have a Scimitar se5a axle but cannot fit it. Any help?|||what mates you think that the S axle will cope anyway. ????