When I bought one of my vans the previous owner had removed the CAT, the
bumber and such was still very hot to the touch and could burn you in the
heat of the summer.  In reality it is the placement of the muffler and such
right next to the bumper that is to blame.  Seems to be better on latter
year vans though.  When I did an engine conversion I routed the exhaust
differently then stock to solve the problem you're having.

Dave K.