I just installed the Bowtie Overdrives transmission crossmember and it was very simple. You can use a TH400 crossmember but it blocks the pan and access to the transmission filter. I feel the money spent was worth it.
TH350 crossmember won't work with the 2004-R mount:
Couldn't have been easier, plenty of clearance for exhaust:
BenNSB, I have been looking for a long time for a crossmember that wont block the pan on the 2004R and you say this one wont? What is the part number of this one you are using so I can get it? I have problems with mine blocking the very back of the pan and making it hard to tighten a couple of the pan bolts.