It is indeed a rare “oldies components” that you’re trying to put together…
Here is the current status with the components:
Starting with HP adapter “HP IB 4X DDR Conn-X PCI-e G2”
It’s a very old (~6 years) HP-branded “ConnectX” DDR adapter, that Mellanox declared as EOL (end of lite) many years ago. meaning, no HW & support available
In addition, there is no Mellanox WinOF driver for Windows10 that supports the old DDR HP/IB (ConnectX) adapter. The minimum adapter type required is ConnectX-3 (FDR)
Flextronics switch - again, very old IB switch not supported by Mellanox anymore
Bottom line:
I don’t see any option that you can “tailor” or setup a configuration where you have Win10 to work on IB over the Mellanox EOL components, simply because there is no compatible river & FW that support mutual workability over the old components
The same goes with Esxi servers.