The bit you put back in is called a 'tie-bar' and it effectively holds your torsion arms into the beam tubes whilst still allowing them to revolve.
The tie-bars don't provide any springing (unlike your torsion leaves) so you replace your shocks for 'coilovers' which provide the means to 'lift' the front of your van and also provide the damping.
If you kept your torsion leaves in AND fitted coilovers then your van would be very over-sprung and would be undrivable.
The spring rate in your http://www.red9design.com/index.htm coilovers has been specifically chosen to give you the very best ride possible if you leave the og leaf spring in place it will counter act the coilover resulting in worse suspension. It would be nice if you could just swop your shockers for coilovers but lets face it, its not that much extra work. At least you can leave your beam in place.