you cant install lt's with the midpipes you have right now (divorced or not) stock headers are called shorty's because they are just that. they are short. they come right off the engine and gather and attach to the midpipe within a foot of leaving the engine (more or less)
longtubes on the other hand, come off the engine and the separate pipes (from each of the cylinders on each side) dont collect until 2.5 or 3 ft off the engine. the collector ends up under the car like this:
so in order to install lt's you will need shorty midpipe (or modify--cut--your current midpipe) which is why we said lt's and an o/r H. the o/r H would have to be specifically for lt's because it has to be shorter than normal midpipes since the lt's extend alot farther than stock shorty headers.
SO, you will either have to cut your stock cats out and then you can use the rest of your midpipe (and weld the flanges on to connect to your lt's) or you can get a new midpipe (a shorty midpipe for lt's) and get highflow cats for it (or just delete the cats all together)
make more sense now?