The RP06, aka Memorex 667 aka Merlin was designed for the 360
IO bus, preursor to SMD. Change the cards, and you had standard
SMD, or IBM tag/data. The 667 was a wonder in its day..

The RM05 and RM02/3 are CDC drives. The cables to MBA are near SMD.
Unit number is not needed in the drive, but it IS passed from
the drie to the MBA, but the signal is inverted, hence you need
black unit number plugs, not blue ones. The other oddity is that
the MBA must be able to select either 512b or 576b data sectors,
but no other size. SO there is some haackery to do that. Think
it is 2 or 3 ccards different in the set in a CDC drive.

The PR07 is a very different beast. It has an in unit uP running the
thing. So you need to change it, and fit one or 2 massbus interface boards.
That means a backplane change. The PR07 filters kill them. The originals
used a coated glass filter, and it would send bits of glass fibre into
the HDA :( Univac did an EO that replaced them with Goretex based
filters. Spinning up 4 at once is real fun ;)