I used Tank Strip paint remover, and then a wire wheel on a bench grinder and it removed it easily with no problems, i have done about 4 cases like this
But they haven't been going broke for at least 10 years so surely they can now buy some etch primer now? My little KTM engine cases look like new...
On my engine restoration I used Por15 - Aluminium colour. I wouldn't do it again though, next time I would definitely look at Cerakote.