Lifter Clatter

Solid lifters are used on Hyd cams all the time in NHRA Stock Eliminator. It's a major reason those fly like they do. However, some lash is necessary to get away from base circle runout, expansion etc. Furthermore, Hyd 'seat' specs are at .006 lobe lift. and profiles are favorable for the HYD/less than solid lifter. Gentler ramps. connect those dots...

Solids have a 'clearance ramp' to gently 'take up' the running clearance or lash for the same BC, Expansion reasons. Solid seat specs are typically in the .015 - .020 lobe lift range even though recommended 'lash' is in the .022 - .028 range. These parameters are squeezed on 'tight lash' solids.
Rate of lift is more aggressive on solids cause the lifters don't the 'problems' the Hyd cousins do. the pushrods take that beating..

Your OEM roller lifters will have to be modified in the 'check' or 'valving' inside the lifter to make them hold under pressure. Or at least disassembled to verify the integrity of the 'check' system.
But I suspect you may be having some pressure issues.. Even just a slight amount of cavitation will severely compromise a Hyd lifter under power.
My 2cents anyway. for what it's worth