The drilled-through holes are countersunk for the four reused longer mount screws.
T mount is aligned with the marks made earlier so that the top of the lens is mounted on the camera correctly.
Once the screws are threaded through and tightened, infinity focus can be checked.
If focus is off "long", a small amount of material can be turned off the T mount.
If focus is off "short", shims can be improvised with paper between the lens body and T mount at the screw locations.