It is basically a direct swap from old to new (prochamber)...
Spray some liquid wrench, wd40 etc...on the bolts to help you loosen them up...
I pulled down the old H with the 02 sensors still connected to the pipe because I just unplugged the sensors...then I placed the 02 sensors to the Prochamber...
Also if you get a Prochamber check it over and make sure there is no "missed" welds that could lead to an exhaust leak...
Remember to get the driver side stud...
A friend helps a lot on the install...to hold the pipe for you, etc...
I used the Dallas Mustang MIL's (plug and play)...and had no engine light and ran fine...seemed to run a bit rich after the swap but I can't complain at all...
Well since you have a 99 you will need it as far as I know...
There are two manifold studs on your manifold that are used with the nut to bolt the manifold to the h-pipe...
If you don't replace it (the stud has a spacer on it)...it will cause a leak because you can't seal it up completetly...I think the NAPA stud part number was mentioned earlier in this thread...if not do a search and it should come up...alls you do is take out the stud with the spacer on it and put the new one in...