An assembly for mounting a circumferential shroud to a casing, including a plurality of arcuate shroud segments collectively forming the circumferential shroud. Each segment includes a circumferentially extending wall and a channel extending from the wall. The channel is receivable in a hole passing through a circumferential casing and has a first connector. A fastener has a head and a shank, which is receivable in the channel and has a second connector that engages with the first connector. A first spacer receives the channel and a second spacer receives the shank and sit adjacent the head of the fastener on either side of the casing. The spacers can be selected to adjust for optimal radial positioning of the shroud and of probes received within a space defined between the casing and the shroud for monitoring rotor speed and the tip air gap of a turbine rotor contained in the casing.