You'd nerf the missile damage - It might be comparable to a normal Tornado round or a little less (like 30-40 net damage instead of 50).
The intent of the missile also would not be for direct impact, but exploding near and around the target, like the Infyrno does already. So, for balance you might make guidance half-way between the Hornet and the Tornado. You'd also give it a long reload time.
...And yes, this would still be a freakin' scary weapon to get shot at with. I just brought this up as we were talking of a better, more unique weapon set for the Shivans (like light bombs, etc.).