RCD BBC Gear drive install/backlash

Looking for some help. BBC blown alcohol refresh. Donovan block had been line honed previously. RCD gear drive installation standard gear will not fit obviously. A 10 under gear fits however there is zero to perhaps negative one backlash. Questions 1. What should normal backlash be for a rcd gear drive install ? 2. How is backlash checked precisely in order to determine correct undersized gear to order/have made (8-12 weeks for rcd to make).?

 

Milodon used to have you set theirs up with a piece of paper run through the gears for proper backlash. I just measured a sheet of paper and it was .0035. Hope that helps.