1. Are these your files generated from a CAD tool? If yes, I would strongly encourage you to re-export the Gerbers as 274X and everything will be fine. However if this is customer generated data than we can proceed by updating the Apertures.
Note: The old Gerber 274D format (from the 1980's and before) is obsolete and deprecated, plus strongly discouraged by the PCB industry - due to potential operator errors and misinterpretation. For example, the aperture list just states THER (without any further parameters -- # of spokes, width of spokes, etc.). I do not believe the Thermal should be 4 lines as shown in the Gerber viewer. IT should have the following appearance.
2. A generic Thermal will have 4 spokes (at 45 degree angles) and the spoke gap width will be equal to 1/2 (OD-ID).
Here's a tutorial how to perform edits on FAB 3000 to add Thermal:
Note: We have updated FAB 3000 to automatically add 4 Spokes and assign the Gap for 274D Thermals when no parameters are available. This will allow you to easily import all 274D files and get the desired thermals your require.