First of all, hl1 engine is a modified quake engine... what does this mean? simply put, alot of the game features from playing hl single player, dosent work in the quake engine.. f.ex. all the sequenced/scripted events that happens during gameplay.

Second hl1 engine is closed source, so we dont have access to whats needed if a port was to be made.

The only way would be to write a new engine, that simulates what happens in the hl1 engine and uses the original content.. and that is hard work.. very hard indeed...