FWIW I ran the exact same cam with Comp 901 springs (single with damper) and stock retainers with no problem. Totally different rocker arms, just saying I don't think you need the dual springs Lunati recommends. I think they call for their same dual spring for the voodoo cam that is a step below that too. Before I set mine up I looked at all the other cam manufacturers and no one else was calling for a dual spring for the cams in the 60403's duration and lift range.

What retainers are you using? In the pics you posted it almost looks like the retainer you are using is wider than the spring itself. IIRC retainers are usually slightly smaller diameter than the spring OD. It looks like you're pretty close, if that's the case a smaller retainer diameter may get you where you need to be.