Just put a straight O-320 together for Lance. We opted for a new cam and lifters along with new ECI cylinders. According to Lycoming service data you have to replace the accessory case when going to a single piece cam/gear because the slinger ring is different. I found that Divco who does all my crankcases can modify the accessory case from a two piece cam/gear to accept a one piece cam/gear. Cost was $160. Here are some pictures.
Original accessory case for two piece cam.
Original two piece cam/gear.
One piece cam/gear not fitting the slinger ring that is riveted to the accessory case.
The newly machined accessory case for a single piece cam/gear.