I'm looking to create a new mod which is along fairly similar lines to the LTN Combinator. I was hoping you could let me know if it's acceptable for me to borrow some of the code? I notice the mod package doesn't include a licence file.

Yeah, probably aught to add a LICENSE file to the mod package itself. It is MIT licensed (as noted on the information tab). So, you can do whatever you want with it. Was there a particular feature you were looking to add to this combinator, or something completely different?