When I put my GT40P in my 66 I read up on distributor gears as well as spoke to several company techs from MSD and Ford. I don’t believe the Melonized gear is compatible with the 8620 used on mechanical roller cams, the 8620 is too hard. I think you’re limited to the brass and possibly the composite. Not saying this is the case with Shaun but I think a couple problems in general are that people don’t verify the correct placement of the gear on the shaft. I bought a Melonized MSD gear and MSD supplies specific info on locating the gear as well as Ford Motorsport. I checked a couple of old Ford point distributors I had and non of them were close to being right. Oddly enough a Auto Zone Taiwan made Duraspark I bought for a 85 Mustang with roller cam was almost dead on. We should be checking gear mesh. I think another general fault is how many people just stab in a new distributor without putting a break in lube on the distributor gear?If your cam is 5150/5160 induction hardened steel or 8620 carburized billet, you might consider a melonized steel gear as an alternative. If you are using a high volume or high pressure oil pump, the bronze gear is very short on useful life.
SADI cams do not need a special gear. A standard cast iron gear is fine. A SADI cam is made of ductile iron and only the lobe surfaces are hardened and this can be done on the production line without changing the profile dimensions.