I plugged my borrowed DDS drive back in, so I now have:

aha2 at isa0 port 0x230-0x233 irq 12 drq 7
aha2: model AHA-1540A/1542A/1542B, firmware 0.5
aha2: sync, no parity
scsibus1 at aha2: 8 targets
st0 at scsibus1 targ 4 lun 0: <ARCHIVE, Python 28454-XXX, 4.44> SCSI2 1/sequenti
al removable
st0: drive empty
st1 at scsibus1 targ 5 lun 0: <ARCHIVE, Python 02779-XXX, 6280> SCSI2 1/sequenti
al removable
st1: density code 0x13, 512-byte blocks, write-enabled

and I noted that ARCHIVE, Python 28454-XXX is listed in scsiconf.c as
not supporting LUNS.  I tried replicating that for the 02779-XXX
but it did not appear to make any difference.

So I had a look at the quirks in st.c and tried adding it in there:

--- st.c.old    Sun Nov  9 00:25:07 1997
+++ st.c        Wed Jun 24 00:21:11 1998
@@ -239,6 +239,13 @@
                {0, 0, 0}                               /* minor 12-15 */
        }}},
 #endif
+       {{T_SEQUENTIAL, T_REMOV,
+        "ARCHIVE ", "Python 02779-XXX", ""},     {0, 8, {
+               {0, 0, DDS},                            /* minor 0-3 */
+               {0, 0, DDS},                            /* minor 4-7 */
+               {0, 0, DDS},                            /* minor 8-11 */
+               {0, 0, DDS}                             /* minor 12-15 */
+       }}},
 };
 
 #define NOEJECT 0

which was take 2, (first just had 0 for the density and 12 for the
quirks, but in both cases when I try and read from the tape I get:

Jun 24 00:15:57 zen /netbsd: st1(aha2:5:0):  Check Condition on opcode 0x15
Jun 24 00:15:57 zen /netbsd:     SENSE KEY:  Illegal Request
Jun 24 00:15:57 zen /netbsd:      ASC/ASCQ:  Invalid Command Operation Code
Jun 24 00:15:57 zen /netbsd: 
Jun 24 00:15:58 zen /netbsd: st1: cannot set selected mode

so random frobbing of the kernel is not going to get this thing
working... any pointers to doco that might help suggest what is going
on?

Oh and this is still 1.3/i386

Thanks.

--sjg