O2 probe swap
 

After some wrestling and a lot of Eezit' type oil managed to remove the old sensor
causing some damage to its threads.

suspect its caused some damage to the Cat threads on its way out too,
as the new part refuses to begin threading in properly.

whats the best fix in this situation,
grind out threaded bolt head on cat and weld in a new one
or look for new cat?

You can get O2 sensor bung in stainless steel. Search on ebay or performance parts stores.
Drill to oversize upside down to remove threads on original hole and weld in the new sensor threaded bung.

http://forums.pelicanparts.com/uploa...1190900597.jpg