Chris,
If you read Randy Smiths "Care and Feeding" article that is pinned to the top of this forum you will see that for the iron engines 25% - 50/50 is his recommendation. I have used this in several older Fox engines and it works fine. The 22% works for ABC/AAC/ABN ball bearing engines. I have used this in engines that were always run on castor and it is fine, never really gets all the castor out of the parts.
Best, DennisT