Look for 6378 boardview /schematic .

Find a variant with isa.
Compare to one without (pics or schematic)

Look at what is missing. It is probably just a few pullup resistors.
Possibly a mosfet for -12v.

Adding the ISA slot might be possible.

The AGP slot on the ones missing it not so much - the intel “extreme” graphics IGP in the north bridge usually takes it and does not expose it to the outside. (In those cheap dell and compaq office pc’s with the pentium4 and the three pci slots, for example) Another version of the north bridge chip that costs a few cents more does, it looks like they use the same pcb for both and just omit some parts where not needed.

If there existed a variant of the board with ISA slot then restoration is likely. A high resolution picture of the board with ISA slot would be useful to determine any missing parts. Check version of the board with and without the ISA slot. If it's the same then probably just the ISA slot is missing. Could be an interesting fun project for someone who has the tools to add the ISA slot back.

With some boards you'll have to add an ISA bridge chip (e.g. IT8888). The BIOS might have to be changed too.

via VT82C686B southbirgde has ISA .

Btw the first schematic is available with minimal searching

I can probably find the p2b in kicad if you want it.

See sig for generic p2b