The valve lifter problem is almost certainly because the little lifter cam on the end of the shaft had rotate past the rocker arm (the reason the owners manual
says not to use it at high rpm). The 'hard' thing you feel is the cam coming up against the inside of the rocker box. Only you are 'highly skillful' (read: 'lucky') and can rotate the came back onto the cotrect side to act against the rocker, the only option is to lift the rocker box to rotate the cam to the correct orientation.
To the lift the rocker box, unless you have screws from the top into the head (convenient, but offensive to engineering purists) or can get the rocker box studs out from the top (generally unlikely), you will need to lift the head off.
How do I know this? I had exactly the same problem on my DBD, fitted with nice stainless rocker box studs and nuts....I lifted the head to remove the rocker box and reinstalled it with cap screws..aginst my better judgement, but more convenient...exactly as my BB34 cam to me with meany years ago!