Tom:
You know that the first byte in the sector 0 MUST be a $EB. OK ?.
Well... if you read the sector 0 ,address 0 and do not found the $EB
then you read the addresses $01C7 (high byte) and $01C6 (low byte).
If the value in those addresses is $0040 then you multiply that value by
$0200 = $8000. That is the absolute address where the Boot sector is located, (Sector $40, in that case.).
Then you can read in that sector , verify the byte 0 as the $EB and read
all needed parameters, keeping in mind that your card has a offset of
$8000 bytes.
I hope that helps...
Ruben de la Pena