RD54 is Maxtor2190, look that up.
The RD53 is a Micropolis 1325 with a fumper installed in the empty R7
location.
Now, heres the nasty part. Of the RD52/3/4 disks there
are Quantum,
Micropolus and MAXTOR drives non DEC branded. They are the same. They
are also different! The NON-DEC supplied are not formatted to match the
RQDX2/3 controllers. So if you find some D540s, you may also have to
format them... you likely don't have diags to do that. So even with a
pile of them your still not ahead.
Solution: prevail on someone that bas a Qbus PDP-11 with diags that can
format the drive.
Also they will have to be done manually IE: do not try to use the automatic
option.
I do it frequently for commercial customers. Often enough for me to
dedicate a BA123 primarily that use.
Dan