At 20K, that's a judgement call. HD recommends checking or replacing at 25K. With that being said, I have 42K on mine, and they make no noise, nor are there any issues.
Inspect them when doing the cams. Make sure there's no marks on the rollers, side play with the rollers/needle bearings, or scores on the roller or tappet sides.
$120 isn't a lot of cash, considering the time and possible damage that can result with a lifter going south. There's no more replacable lifter blocks and tappet failure now could result in a trashed right side case half, and a $329 oil pump.
Too boot..... you're placing lifters with 20K on a new cam, that now has taller lift, and more duration, which equated to more pressure on the lifters.
“When the going gets weird, the weird turn professional....” ~ Hunter S. Thompson~
R.I.P. Rubberdown. 1971-2012
2005 E.G. Classic
Baisley Oil spring
Rinehart 3.5" pipes
S&S adj pushrods
3 stickers, adding 5 hp each. I swear......