Measure the open area on the bow before you go shopping. Is there space between the forestay chainplate and other deck hardware? The websites usually do a good job of posting the measurement diagrams for the rollers. If you can hold them in a store, that is even better. I found the roller I wanted: length, width, features online at Defender. I cut it to fit around my bow cleat. This is on a 272.
When you measure and mount, take into account the flukes on your anchor: you will want to mount the roller forward enough to hold the flukes off the bow, but be sure you still have plenty of base projecting onto the deck, so you have a solid mount.