Get a picture of the gear side of the starter with the tape measure.

What is the thickness of the mounting adapter where it bolts to the flywheel housing?
Starting from the original drive end housing with 4" length and 2" to face of flywheel. To get 1-5/8" the starter would need to move out 3/8" and that would be the thickness of the adapter.

The assembled parts of the Auto-Lec look right but I can't tell about dimensions. The thickness of the piece between the starter lever housing and the adapter looks thick to me. The original DEH flange thickness is 0.715".
Hard to tell how they juggled the dimensions.

Found some notes on a 3T starter installation.
Flywheel face to front of housing 1.771"
Face of ring gear to front of housing 1.445"
Ring gear is 1.260" thick.

With those dimensions the adapter flange would be about 0.555" thick or probably a 1/2" thick plate.

Seems you have a flywheel problem????