Hi Nigel,
Acrylic requires a specialist solvent glue - something from the WELDON range will do a perfect job.
WELDON and similar solvent glues are available in a range of "thicknesses":
1. If the original acrylic parts are still a perfect fit - then use the thinest glue - Weldon 3 or Weldon 40
2. If the parts don't really fit, then use one of the gap filling solvent glues
3. If you need to bridge missing pieces, then one of the two part acrylic glues will do the job - these chemically react to create new acrylic material.
And you need to take care using these glues - follow the instructions on the safety data sheet. They will bond skin instantly (wear thin gloves - like those on fuel station forecourts) and you may be sensitive to the solvent fumes.
The "welded" material will be as strong as the original part - but don't leave any cracks untreated - they will start a new crackline.
Robert