Finally, a successful modification of the commander's cupola to get rid of the original cupola and replace it with something less conspicuous.
Ground away carefully the original cupala.
Applied a bit of 2-part epoxy putty to the area under the commander's sight. This turned out to be a benefit and a hindrance as it did not adhere to the plastic and fell out while sanding and enlarging the hole created by removal of the cupola features. This was fixed by sanding the area inside the turret and applying CA glue before putting the epoxy plug back in place.
More sanding and carving again to create a larger hole and then to the bag of parts containing circular shapes to find something to use as a collar on the turret roof to cover the oblong hole shape I had created. The new collar part was modified to fit and the inside diameter was increased to allow the M113 cupola to fit comfortably within. This has brought to me much happiness and joy since this is my third attempt at this modification. Third time is a charm?
Attached images with and without cupola