How much lift will the stock lifters handle?

IDK the answer to your question.
But I can tell you that if you run in the bottom of the lifter, you have a lotta lotta room for the lifters to pump up if the springs cannot keep it together. I think they have a range of .095 or something, and at the valve that is .095x1.5=.143, so if you don't have the room look-out!, you could be buying a new engine; jus saying.

I run an adjustable valve gear and a preload of .020, for exactly that reason.
You could just order shorter pushrods to fit, and then no worries.The trouble with that is yur married to them, but that's probably not an expensive decision.