The nice thing about Sea Vixen is that, in order to fit it into the Sea Harrier, it was deliberately made distributable using a databus, so that the whole weight of the thing didn't have to go in the nose. Many of the radar black boxes were actually in the rear fuselage. That feature might ease integration onto the Lightning, since the latter's radar has to live in a very tight pod in the centre of the intake. Having said that, Lightnings didn't have much space to spare of any sort anywhere, but if you were getting rid of Red Top, the missile support pack would become available without losing the pylons, since any modern weapons you put on them would be much less "needy".
Actually, kind of solved my own problem there: put modern electronic systems in the missile pack area, stick a TIALD on one side and a self-defence AIM-9L on the other, OR, in a slightly earlier timeframe, it should be perfectly possible to "pod" the Jaguar's LRMTS and put that on one of the fuselage pylons for the CAS role.
Here's another possibility: missile pack avionics upgrade with pylons for two Mavericks...
They're about 30% heavier than a Red Top, but it should still be doable, and they can definately stand being carried on a side rail because there's a triple launcher or them that carries two just like that. You'd need a TV screen in the cockpit, but if you're updating the radar to a modern one with a CRT display anyway....
Just remembered: Switzerland integrated Maverick on the
Hunter, so if that's possible, it should definately be on for the Lightning.