I will try to be more clear or complete.
The Speedmaster heads are basically copies of Edelbrock LA heads. The rocker shaft stands are in the same location as the Edelbrock heads.
The Speedmaster stainless rocker arms are basicaly copies of the Comp Cams stainless rocker arms. I have both sets, measured them for comparison, and they are dimensionally the same.
The retainer contacting the rocker arm happens on Edelbrock heads with Comp rocker arms too. So this is NOT specific to Speedmaster parts.
The reason previous posts said to correct the geometry first using a kit from B3 racing is because the rocker shaft stand positions the rocker shaft too close to the valves and too low FOR A ROLLER ROCKER ARM. That is usually the only cause of the interference. So if you get the measurements from B3 Racing website and call Mike with that info he can make the kit properly. It is not just shims. It is usually an offset shim to move the rocker shaft up and away from the valves a specific amount based on your measurements. Some are considerable. Once kit is installed you can double check for the interference. Usually there will be plenty of clearance there with the kit installed, no rocker arm grinding, no beehive springs and no small retainers.
The Trick Flow heads moved the rocker shaft position. That is why guys with Trick Flow heads are not reporting all the clearance issues. They require much less correction.
Lastly, once you install the correction kit you will likely have to add clearance for the pushrods in the cylinder head.
Sorry for the long post. Just trying to be clear and cover it all in one spot.