It is totally possible to use the Authoring Kit to create SF or PF2. The Authoring Kit lets you get access to the core skeletal files of HL and gives tremendous power and flexibility to design what you would like. Its the same tool that LW used to create all the HLC game systems. This is the good news.
The bad news is that the power and flexibility comes at the cost of understanding how to program in HL scripting language. You will have to self teach yourself 80% or more of the software and many things like Agents have no examples in the open game systems. Using the Authoring Kit will also require that you work in the RAW XML files as no "editor" exists for this to happen.
To be clear this would be a
Daunting 
task for anyone to take on and you would need months to just build a functional framework. That does not include inputting all the data once the framework was working.