That is probably the best way forward, however sourcing a used amp sleeve may be not be that easy as most would be standard width, (19"), and then 1U, 2U etc. etc in height. I've got a new 2U one but your head is too wide.
The cabinet is a different situation as either modelling the driver, or a quick call to Ashdown, and you'll know what size cabinet it will work in. If the cabinet surrounding the amp head is still intact, you could just cut that off as a start.