Although you may be able to make a size 4 missile that is nothing other than a stage for the four size 1 missiles.
It's been awhile since I've played though, so I can't remember if subsequent missile stages need separate targeting or can still use the fire control of the ship they came from, but I think that the later is possible.
There is a small chance that you can't make a missile with zero engines and zero fuel, if that's the case then you'd still be able to make a size 4 missile that wrapped three of those size 1 missiles.