hey guys can someone tell me what these plates/irons are out of? They were with rx4/5 (74-78) 13b housings (large MAZDA in boxed frame) are these the original irons for these housings,the intake runners and port sizes on the centre iron look similar to the 12a Y type but are stamped N (all my irons are stamped N not just centre) they don't seem to have been ported. So would just like to know if these irons are original with the housings or are from a 12a? What car they came from? Or if anyone else has come across them? Any help would be greatly appreciated
pics in the link below thanks

Front Irons/Plates https://imageshack.com/a/xYiz/1
Centre Irons/Plates https://imageshack.com/a/AYiz/1
Rear Irons/Plates https://imageshack.com/a/nYiz/1
Complete https://imageshack.com/a/dYiz/1