If you think you have one or two lifters that are collapsing, or not filling with
oil, take the lifter apart, clean it real well with gumout spray. An overnight bath in laquer thinner and some steel wool scrubbing will remove stubborn deposits.
My preferred way of pre-oiling lifters under pressure is to slide the lifters in the lifter bores, make sure that they rotate easily, then with an electric drill and the distributor removed, and a few quarts of
oil in the pan, prime the engine with
oil from the oil pump. Wait until the air bubbles are all out, push the lifter innards down with a pushrod, or screwdriver several times until the lifter won't depress from the retaining clip. Then turn the engine over by hand so that each lifter is sitting on the bottom of the cam, and you get full tight on all lifters. Then, button the engine up.
When installing the rocker arms, follow the firing order so all cylinders are at TDC on the firing stroke as you install the rocker arms. Twist the pushrod with your fingers as you tighten the rocker down. The pushrod will stop turning at zero lash. Follow your cam manufacturers instructions for lifter pre-load. Typically this will be 1/2 to 1 turn past zero lash.
Having gone through all this, if the air hasn't been bled out when you first start the engine, the lifters will clatter like hel! for 20 - 30 seconds, then stop as the lifters fill with oil.
If you have a lifter that just won't quiet down, replace it. Or replace the whole set if several are causing you trouble.
Ideally, you should be using lifters from the same manufacturer as your cam, and they should be the lifters specified by the cam manufacturer for your specific cam. If you need one or two replacements, they can be ordered from the cam manufacturers tech support staff, and if this is a new cam and lifters, they should be free under warantee.
Hope this helps.