What is the best was to quiet lifter noise on a 1991 Jeep Wrangler with a 4.0 engine?

My '91 has a new engine, but they used the old head without a rebuild. I had some lifter noise, which is normal with the 4.0. Recently it became a little noisier, and I drained a pint of oil, replacing it with a pint of Marvel Mystery Oil. Within 30 miles it was much quieter. From what I understand, MMO has solvents that clean out the gunk that cleans out the passageways in the lifters allowing them to maintain pressure. I would bet that almost any lifter solvent/cleaner would do the same thing. I use MMO because it's worked for me before.