ok this will take a bit of searching but here goes
Half-Life: Opposing Force Version 1.1.0.9
half-life 1.1.1.0

filenames i installed
hl1110.exe fileplanet
opforup.exe unknown dropped by hl1110.exe into root half-life folder
i have no idea how to roll back to half-life 1110 from steam because i have never installed steam half-life or have no intent to install steam EVER