I am in the process of changing out the cutting head in favor of a spiral cutter from Byrd. I paid about $600 bucks for the head.
Be careful when trying to remove the head from the gear box there is a screw in the end of the hollow shaft that has to be removed. I took this to a machine shop and he pressed it out and broke the screws out of the back of the box and ruined the pinion gear. All of these are replaceable but it is obviously better to not break them in the first place. Also on older models you need to have a seal change for the main shaft. The seal is 1.050 to 1.057 od this remains the same. The new shaft has a seal OD of 1.037 so you need a seal a bit smaller. Grizzly sells this seal for $12.00 + shipping. It is best to just order the seal if you are not sure you will need it or not.