Just boot to the dos prompt, and use debug ( should be there on the disk) and you can use the drive bios direct to setup the disk. From the days before you had a bios over 64k, and had a rom for each board. I probably have memory for that board in my bag of older memory, though they might be SIP modules.
Just think, that those asics and other glue logic took the place of around 30 40 pin DIP packages, the original AT design had a lot of them. The buffers were definitely needed, as the 386SX was pretty poor at driving any bus, it really needed a buffer right next to the chip for anything other than driving a single companion chip. The only difference between the first SX and DX chips was that the DX actually passed the math processor check, so then one pin was pulled high to enable the coprocessor. If you were willing to chance it you could use a SX and simply change the jumper that turned it into a DX, and hope the processor was more or less functional. Never was able to get a working one though.