I have an older Security Chimneys BIS with a 7" ID factory chimney system. I have been thinking about yanking the BIS out and installing a free-standing stove in its place. Am I able to adapt a newer 6" EPA stove outlet to this chimney or do I need to start from scratch??? From what I have learned on the Security Chimneys website the Secure Temp ASHT is rated for 2100 deg F. However this system is 20+ years old so I'm not sure if it was manufactured to the same specs back then. I'm guessing it would be next to impossible to line a 7" pipe with a 6" SS liner, correct? Any input would be much appreciated...