Assembly visualisation gives volumes of each component. you can export the report in EXCEL and sort by volumes
However, it does not give volume info for bodies in parts. Therefore you should first save all bodies as individual parts and insert them in assembly
Another way is to use macro from Beta version of #TASK
It gives a raw report of volumes for all bodies (input can be multibody parts or assemblies).
You can also use this report to group volumes and understand the number of repeated bodies
Please note that both tools give you only volume. If parts are mirrored (and considered as different parts) they still will have the same volume.
Hope this will help
I'll give this a try if my customer can't provide step models from the catproduct directly.