I've been working on a timing problem with a MP 380HP Magnum crate motor. Problem is valve timing. I've discovered EXCESSIVE lash in valve train. I'm talking 1/8" play in the rocker arm. Dial indicator reals extremely shortened duration and accompaning reduced lift. Cam appears to be installed on correct index, just shorten duration. Don't know how, or why, anyone would do this. I purchased the car last Fall, and just now getting into the discovery phase!
Should I be concerned for some deeper poroblem with hydraulic (roller) lifters colapsing, or... can I simply tighten the rockers down and see where that leads.
Thoughts, opinions please.

if it has the stock magnum rockers, the bolts in the center should be tight and bottomed out..if they are loose, that is a problem.

Are you running your tests with a temporary solid lifter?

If so,
what is that temporary lifter's length?

There was a problem and TSB put out for the early years of the factory hydraulic roller lifters first used in the 3.9/5.2/5.9
I think the factory was putting out a revised design of hyd roller lifter by 1994.