As title suggests... Have extra 5TH Gen Engine with approximately 17K miles as a spare. Have a '99 and an '04. Have 6TH Gen Throttle Body/Injectors; understand the injectors are different along with the wax unit as compared to the 5TH Gen. As the fuel pump assembly, the air cleaner assemblies are different part numbers. For a '99 build or long term spare (or maybe even a 6TH retrofit): 1) Is the throttle body of the 6TH Gen compatible with the 5TH Gen (what needs to be done tuning, fitment wise)? 2) Are the air cleaners (boxes) interchangeable? Since this will be mostly for a spare or naked 5TH Gen build in the future, if interchangeable, are there any interference points such as with the gas tank? Thanks guys, slowly but surely making progress on the harem (two mistresses maybe with another on the way). Build thread coming soon, ummm, hopefully.