Can I put SF6 in the AC system that is original to my 90 5.0 LX? If I cant, do i need to replace the system or is there another modification that allows a freon based system to use SF6 like seal changes, etc... ?

 

Sulfur hexafluoride? No. Where did you get the idea you could?

 

Sorry I used a designation for our systems that we recharge on the equipment where I work. - Substitute Freon-6. But what I am asking is whether or not I can simply recharge a system with the latest Freon replacement or do I need to replace the entire system?

 

Typically, a system designed around one refrigerant is not compatible with a different refrigerant without some modifications in either lubricants used, compressor used, and/or hoses/seals used

I’m not familiar at all with the refrigerant you’re referring to. This link has info on what is the latest type of refrigerant for automotive.
https://www.vehicleservicepros.com/s...ants-to-r-134a