Look on the end panel for the kit's model number, such as "RC-15" or such.  Back then, the kits were either in a white corrugated box or a red one.  The "white" became "yellow" as the cardboard aged.  A lot of TF kits wound up in red boxes in the later years.  However, the kits basically didn't change.

Now, there are a LOT of differences between the original Top Flite scale kits and the current Golden Editiion kits.  The  new ones are completely-different designs.