Speedmaster Stainless Rocker Arm Issues
Here are some other threads.
Post 20 in this one shows Edelbrock heads with PRW stainless rockers and same retainer interference:
Correcting Mopar Valvetrain Geometry
Post 34 in this one shows how one of the measurements is taken for this kit, then in post 43 you can see how thick and how offset this particular combo needed the spacers (spacers visible under shaft):
Valve train geometry
This thread shows pushrod interference in post 1 and clearance added in post 19:
Pushrod Rub (Intake side of head)