What's the advantage of using an L8?

I need an ECU for my 4x4 Cossie Cortina project and not sure if I need an L8 or not.....L6's are cheaper as you know.

Do I need to use an L8 for the 4x4 lump? I have a L8 MSD chip for my set up...will this fit in an L6?

Cheers!