Sorry, 303, I think you have your turrets mixed:
The Cadiallac Gage T50 on the V100 (&V150?) was the second turret used on Australian M113A1, and it was the improved T50(Aust) turret specially made for Australia.
The first turret used was the Aircraft Armaments Incorporated Model 74C, designed to mount twin .30 cal MGs. Only 20 were purchased as an interim: their installation required no structural change to the M113A1, but replaced the standard CC's cupola. The T50(Aust) was the long term solution that did require structural change by way of a larger hole, concentric to the original CC cupola hole, being cut into the roof.
Interesting pics, by the way.
Mike C