I have those same lifters in my current motor. I called Howards about a month ago for a similar reason, my pushrods felt slightly loose in the lifter cup (VERY slight...probably all in my head). For reassurance I asked them what size pushrods these lifters were made for, and they said they will work with 5/16 or 3/8 pushrod tips. I have 5/16 Smith Brothers oil through pushrods, and they seem to be fine (car runs great, no excess noise).
Anyway, the whole point to that was what size pushrods are you using, 5/16 or 3/8? My guess is the 3/8 is a better fit.
