Thanks for your question. This is a common question as 274D gerber files are less used nowadays (due to being phased out for the past 15 years by 274X embedded gerber files - where the aperture list is embedded inside each gerber file). See the following forum link for more details:
Note: FAB 3000 includes about 50 Aperture rule templates plus several default Tango aperture templates; however it appears that FAB 3000 does not have the specific template to import your Tango II aperture files. Please keep in mind that back in the 90's with each update of their layout software, there may have been slight format changes to their Aperture list file. In many cases a slight modification of an exiting FAB 3000 aperture template will resolve the problem, and in some cases a new Aperture Template is require.
Feel free to send me your aperture list file, and I'll be happy to take a look.