I've called Reincarnation to see if they would sell reluctor plates with 10 degree limiting slots. They will only do it if I buy a rebuilt distributor from them. I recommend you ask for a 10 degree slot if you buy one of theirs. I own a Sun distributor machine and do advance curves for my and some friends distributors. This experience has taught me the 10 degree slot is the best for street small block Ford engines. This article ;http://vb.foureyedpride.com/showthread.php?22229-The-Ultimate-Duraspark-Distributor-Timing-Guide, explains why.