a univibe is a 4 stage phaser. while the univibe was regarded as a failed attempt to simulate a rotating speaker/leslie effect, it ended up with a cool sound of it's own.
the sound of a vibe is a throb or a heartbeat-like sound that is slightly lopsided; compared to the volume modulation of the tremolo, the pitch modulation of the vibrato, the phase modulation of the phaser, and the doppler effect (to my ears, this sounds like a combination of the other modulation effects) of the rotating speaker/leslie.
to use hendrix as a basis for comparison; "machine gun" is a univibe, while "angel" is a leslie.
i agree with niko, instead of modding, just go with a cheapo dano. less hassle.
cheers.