The spring seats will need to be cut falt... so the step is gone. They should have had that done before - I shudder to think what the pressures were with the inner spring on the raised step...
Be very carfeul during the valve job phase. Shaft rockers need the tip of the stem perfectly placed in terms of heights and you are using non-standard stuff. It's not only a matter of the overall length - but also where the valve sseat is created that sets that placement.