Well, it would help to know what your stock ignition is .
MkI, MkII, MkIII?
If it is an 81 caddy like in your profile, then it'll have a vac advance dizzy if it is stock. You can run your stock ignition for sure, but you'll lose the benefit of the vac advance, unless that vacuum port on your mikuni is ported vacuum and not manifold vacuum. I think it's ported...but not sure. If it is, then you can hook up your dizzy vacuum line to it. The spark will fire off fine, but a hotter ignition will help a lot.