If you have a front mounted oil cooler and can actually get the oil drianed from that, and the lines that run up to it, I would say start with 12 quarts. Let her warm up, check and top off. Don't think you would run more than 14 qts unless it is a really big cooler.
914-6's with stock coolers - Start with 8 qts, warm up and top off as needed.
You are right, you don't want to overfill them, they spit it out!