It still sounds like something that could work. If using a controller like the one I mentioned, you also gain the option of adding a light to call attention to the movement, the option of playing an .mp3 sound track, and the ability to program a delay period before it can be triggered again. I am assuming you plan to use a DC motor to rotate the angel, such as a vent, wiper, or window motor.
The way I would try first is using a short tube of some sort (staw, pvc, toilet roll) to limit the field of view for the phototransistor (PT). The PT will take the place of the PIR to trigger the controller. You will need a controller with at least 2 relays, each having a Normally Closed (NC) pin, a Normally Open (NO) pin, and a Common (COM) pin. You will also need two switches similarly configured with at least NC & CON pins.
If you draw the following out it will likely be easier to understand.
One side of Switch 1 goes to +12Vdc source.
The other side of switch 1 goes to Controller relay 1 NC pin, NO pin gets connected to GND, COM pin goes to motor + (positive).
Relay 2 NC pin goes to source GND, NO pin goes one side of Switch 2, relay 2 COM pin goes to motor - (negative).
The other side of Switch 2 also goes to +12Vdc source.
Switch 1 is mounted so that it is activated open (NC pin is not making connection to COM pin), when the angel is in the resting position.
Switch 2 is mounted so that it is activated open (NC pin is not making connection to COM pin), when the angel has reached the attack position.
Both switches should be closed (making a connection between NC & COM) at all other times.
If everything works...
When the phototransistor sees enough light it will trigger the controller.
The controller will change the state of relays 1 & 2, the motor should drive the angel around, until it hits switch 2 which opens and disconnects the motor.
When the interval you programmed into the controller has elapsed, the relays with return to their original state.
The motor will then return the angel to it's original resting position, where switch 1 will disconnect power from the motor.
Hope this helps.
Bobby