I've never had much good luck with aftermarket lifters, either. I would probably just try to clean the ones you already have. I know when I did my 3.0, 11 of the 12 were were stuck solid. a little cleaning in diesel, and they all came back to life.
Mitsubishi Valve Lash Adjuster Cleaning Bulletin


1994 Mitsubishi Montero LS, Stock (for now)
General class license -KF5UHG