Is it possible to select a specific instance of an object for a 3D face to use as a face object?
Yes, you just need to pick a specific instance to use with conditions.
When an instance of an object is being used as the face of a 3D object can I use the attachment points of that instance?
Just the image is used when setting the face of a 3d shape. You’d have to calculate that from scratch.
For example, a unrotated 3dshape with its origin at the bottom center, with the front face set from a sprite. You can then calculate the image point location on the front face with something like:
ipx = (sprite.imagepointX(1)-sprite.bboxLeft)/sprite.width
ipy = (sprite.imagepointY(1)-sprite.bboxTop)/sprite.height
X=3dshape.x +(ipx-0.5)*3dshape.width
Y=3dshape.y +0.5*3dshape.height
Z=3dshape.zelevation+ipy*3dshape.zheight
If the 3dshape is rotated that would be another step:
NewX = (x-xcenter)*cos(angle)-(y-ycenter)*sin(angle)+xcenter
NewY = (x-xcenter)*sin(angle)+(y-ycenter)*cos(angle)+ycenter
Anyways, that’s roughly how it can be done. You’d pick a sprite to use as the front face, set the front face, and calculate the position from that picked sprite on the front face.