One great way to see if a Nova or Camaro came with Bigblock and TH400 is the trans cross member, it should then be the oval tube kind.
I adjusted the brightness of one image in the add and it looks to me as it isn't a TH400 cross member, it could be a crossmember for a 4-speed and they were different for bigblocks in Camaro and Novas, see here:
http://www.camaros.org/trans.shtml#Crossmembers
Anyway it has telltales of being an SS and BigBlock, the heater cover can easily be changed but not many do it.
Jan