Going with longer/wider trailing arms will make a huge difference in your ride
and handling. You can use 2x3, 2.5x2.5, or 4x5 and wrecking yard axles to keep
the cost down. The first two use the early bus IRS axles and the 4x5 uses the
later ~21" vanagon axles.
3x3 trailing arms can be had cheaper but you have to buy custom axles for the
application and that usually puts the cost higher than the other.
With longer arms you should have at least a half cage so you can tie your upper
shock mounts into it. You will need at least bus length shocks and since they
mount to the top of the new arms, the shocks will extend about 10" higher than
they used to.
The longer the arm, the more spring rate you will need to overcome the leverage.
That means either stronger torsion bars or supplemental suspension. The cheapest
would be cheap air shocks or chevy truck coil-over shocks. Next level would be
air bags or torsion bars. After that it is pro air shocks or coil overs.
As with anything it is what you can spend. The nice thing about most of this is
you can do it in stages.