As written at here, the BIOS ROM is a Mostek MK36000 or equivalent.
If that ROM fails, needing replacement, there are quite a few replacement options available to you, and they can be put into two categories. Choose which option is most suitable for you.
Of the various options below, choose which option is most suitable for you.
Due to pin differences, on the IBM Fixed Disk Adapter, if a 2732 (or 27C32) is used instead of a Mostek MK36000 (or equivalent), only the first 2 KB of the 2732 (or 27C32) can be read.
Fortunately, the code in the BIOS ROM of the IBM Fixed Disk Adapter is such that it can be modified to fit into 2 KB.
The modified code for the 2732 (or 27C32):
• First and second variation of IBM Fixed Disk Adapter:
Category #2 : Various direct Mostek MK36000 substitutes
Here, the replacement situation is the same as for the ROM's used on the IBM 5150 (IBM PC) motherboard. And so see the 'Use of an EPROM/EEPROM to substitute' section of here for what options are available to you.
Code to go into the replacement EPROM/EEPROM can be found at here (where the make is shown as 'IBM (Xebec)').
For example, the photo at here shows me successfully using a TMS2564 EPROM (2564, not 2764) as the replacement.
For example, the photo at here shows me successfully using a 27C256 EPROM as the replacement. Undesireable, because the IBM Fixed Disk Adapter will then take up two slots in the computer. See here for a method of quadrupling the 8 KB sized image available online, to get a 32 KB sized image to go into the 27C256.