Pater Martin of The Monastic Channel has posted a video of Midnight Mass in Heiligenkreuz from the year 1979:
As you can see, Mass was said ad orientem. The neo-gothic reredos, which was then still under the ciborium magnum, was moved against the east wall of the church in 1981. It was not until then, three years after the death of Abbot Karl Braunstorfer, who had been a father of the Second Vatican Council (and had had a very clear idea of how it ought to be implemented), that his successor started celebrating versus populum in the Abbey Church. Here is a clip of Midnight Mass from this year– you can just see the old reredos on the sacrament altar through the bars of the grill behind the high altar:
The neo-gothic reredos was a mediocre artistic achievement, and it can be argued that the painted crucifix that replaced it gives the sanctuary more focus, drawing all eyes toward the Lord. Unfortunately, this effect is contrecarré by the change to celebration versus populum.