As noted, v8 does not import 3D models from v7, so such files will need to be either cut using v7, or converted.
Carbide Create has a feature for exporting the 3D model as a height/depth map pixel image:
so do that to get:
Then open the v7 file:
in v8:
Draw a rectangle which matches the Stock Size:
and position it aligned with the Stock area:
Then import the pixel image:
Adjusting the settings as needed:
which then previews as expected:
(note that tab placement may need to be verified/adjusted)