I had to cut off the cat's on my 97 to get the 98 4.6 litre to fit....exhaust manifolds were about an inch and a half longer. It is my understanding that if I don't replace the cat's i will need an O2 simulator...anyone know anything about this?

 

A boss with a threaded bore to fit the O2 sensor will need to be added to each exhaust pipe just aft of the manifolds. Anyone with a good welder can do the job. Finding the bosses will be another story. They could be fabricated from 3/8 inch thick steel stock disks about 1-1/4 inch in diameter, drilled/tapped for the sensors then welded to the pipes. Take a look at the sensor installation on someone's ride to see the mechanical configuration so it can be copied.