Sorry to follow up before anyone has had a chance to point out the
silly misstake I've made, but the following may be of interest. 

I put another floppy in the drive and did:

# gzcat < $S/floppies/kcadp12.fs.gz | dd bs=147456 > /dev/rfd0a 
fd0a: hard error reading fsbn 0 (st0 40<abnrml> st1 20<bad_crc> st2 0 cyl 0 head 0 sec 1)
fd0a: soft error writing fsbn 0 of 0-7
fd0a: soft error writing fsbn 8 of 8-15
fd0a: soft error writing fsbn 36 of 32-39
fd0a: soft error writing fsbn 72 of 72-79
fd0a: soft error writing fsbn 80 of 80-87
fd0a: soft error writing fsbn 88 of 88-95
fd0a: soft error writing fsbn 108 of 104-111
fd0a: soft error writing fsbn 144 of 144-151
fd0a: soft error writing fsbn 224 of 224-231
fd0a: soft error writing fsbn 264 of 264-271
fd0a: soft error writing fsbn 368 of 368-375
fd0a: soft error writing fsbn 440 of 440-447
fd0a: soft error writing fsbn 480 of 480-487
fd0a: soft error writing fsbn 576 of 576-583
fd0a: soft error writing fsbn 616 of 616-623
fd0a: soft error writing fsbn 624 of 624-631
fd0a: soft error writing fsbn 648 of 648-655
fd0a: soft error writing fsbn 656 of 656-663
fd0a: hard error writing fsbn 688 of 688-695 (st0 40<abnrml> st1 4<sec_not_fnd> st2 0 cyl 19 head 0 sec 5)
dd: stdout: Input/output error
0+87 records in
0+86 records out
352256 bytes transferred in 46 secs (7657 bytes/sec)

That did not look too good, a 2nd attempt imediately after:

# gzcat < $S/floppies/kcadp12.fs.gz | dd bs=147456 > /dev/rfd0a 
fd0a: hard error reading fsbn 0 (st0 40<abnrml> st1 1<no_am> st2 1<no_dam> cyl 0 head 0 sec 1)
fd0a: soft error writing fsbn 808 of 808-815
fd0a: soft error writing fsbn 976 of 976-983
fd0a: soft error writing fsbn 1872 of 1872-1879
fd0a: soft error writing fsbn 2240 of 2240-2247
fd0a: soft error writing fsbn 2340 of 2336-2343
fd0a: soft error writing fsbn 2376 of 2376-2383
0+300 records in
0+300 records out
1228800 bytes transferred in 95 secs (12934 bytes/sec)
#

The last line looks ok, but all the fsbn errs are a worry - don't
think I'll try booting that diskette :-)

--sjg