i am swapping my 2004-r for a TH400 (4in tailshaft) on my 85 Monte ss. I have read in your tech articles that a 2004-r length driveshft will work unaltered, but other are telling me that it must be shortened 1/2-3/4 inch. What is the correct answer, and how will I know before messing anything up on the new trans? This is my daily driver, so if needed, I can get a std. length 2004-r driveshaft and have it shortened and ready to install. Any help or experience you may have would be a great help.