Anyone have lots of experience installing slab boxes into beam and block type slabs?

I have done commercial slab installations ... but never a block and beam.

Which boxes are better to use?

Tips and tricks to make sure the boxes are secure and dont move during the pour ... dont fill up with concrete ... how to line it up if the beam is in the centre of the room etc etc.

From experience working with old type slabs ...

Pipes are glued ... a short piece is cut and secured across the coupling and tied to the reinforcing using soft draw wires.

boxes are filled and compressed with brown paper ... then secured using wood strips and screws.

I see there is an albro box ...but not ideal for beam and block type slabs.

It looks like there is a variety of galvanised slab boxes 115x220x 400/500/550 which drop into the space where the block is removed ... but it looks like it could get interesting trying to line up a row of downlights in the middle of a room if the beam falls in the centre.