Thanks for the quick answer, Loco Bill.
I do not intend using the existing track so the connections are not an issue.  So this track I see described as Bachmann-Code 332 -- 30" 76.2cm Radius Section (Makes 5' 152.4cm Diameter Circle) should work, right?
Sorry I still have this niggling concern : could you confirm the rails in this 332 track the same distance apart as my exiting rails, namely 49mm?  Am I wrong in stating G gauge has rails 45mm apart?
Maybe I am confusing G Gauge and G Scale?

Thanks again!

Good day everybody!
I have spent quite a while googling away at the following question.   In 2009 I bought a Atchison Topeka Santa Fe train set with steel rails,  Locomotive is #49. 
I would like to purchase a set of tracks to make a circle wider than the current 4 foot circle. I thought the existing track was G gauge but the distance between rails for G gauge is 45mm and the existing track is about 49mm. 
Is the existing track a proprietary gauge?

Thanks!