Do you me an that the server booted the old Slackware 12.1 installation on the array attached to the Promise controller? If so, that's a BIOS issue. Look for the Boot Order settings
The drives are not visible in the BIOS
My new disks where note visible.
The old disks showed in the new server as "Linux Raid Autodetect" type while executing fdisk.
The new drives do not and have been detected as fs type 83.
I stopped all raid arrays and umounted them.
The I ran
> mdadm --assemble --scan
and used that output to create a new mdadm.conf
That seemed to work.