I don't think it would be too difficult to do. Take the Warlock class and the appropaite classes from your D&D of choice; then use the later as a template to rewrite the former. The Warlock attacks like a cleric, saves like a magic-user, and has thief HD.
There are some invocations that wouldn't work as well in an earlier version of D&D. Beguiling Influence and the grasp invocations come to mind. Luckily, there aren't many invocations.
I'm not sure how to convert some of the miscianleous class features like Decieve Item. I would just cut them. The class has enough going on with eldrich blast and invocation that it doesn't need much more stuff.