Here's what we just did:

'07 Tahoe, AFM 5.3L.

AFM lifters suck!

Replaced with:

2005 GTO lifter retainers. These retainers accept the older style lifters and have the keyed notch in the plastic so that it will sit in the '07 5.3L AFM block.
PN for retainers qty4: 12595365




These are pricey, but I wanted a stock replacement 5.3L lifter. We typically use comp, NAPA, and the LS7 lifters.
PN for these lifters: 017122490

You'll also need a lifter valley cover. I believe the '05 GTO plate will fit as well. Remember to use orings to block off the oil supply ports to the afm lifters.

that's all you need, good luck,

allen