I can't figure it out, maybe you can?

hi the motor is 10 years old? you just don't thow lifters on a used cam !!!
I would look at valve spring pressures. they prob have lost seat pressure, thats why motor will not rev. a weak valve spring can let the lifter pump up.
I been through this before on my 340. you need to pull a couple valve springs
and check them for seat and open pressures. I think you will find the problem