Thanks for the assistance, zhadoom.
I flashed the EN29LV040A by choosing the
option “Pm39LV040 4MB compatible”, and
three months on, my Bytecc SiI3512 PCI card
still seems to be functioning correctly.
Be warned that this Bytecc card has been sold
with at least three different flash chips over the
last couple of years, including a non-flashable
(one-time programmable) chip. So examine any
potential purchase closely if you hope to be able
to modify the firmware.