rocker arm geometry

This is the problem. Your valves are for a MAGNUM setup, not an LA setup. The LA valves are longer than the Magnum valves. This has been an issue ever since they started making these heads. Comp Cams had the right valves for the LA setup, but when they stopped carrying the RHS X heads, they stopped carrying the valves. The PRW rockers work better with the longer valves, the Hughes rockers work better with the shorter valves. This is why you have to use rocker shaft shims on Hughes rockers when they are used on RPM or stock heads.

The lash caps will work, you just need to file them down so they are not so deep.