Pre-cat is def AFR.
I'm not sure of the 2.7, but the 3.4 def. used this.
Lets see if i can dig up the info (got it from Gadget @ URD)
OK here is some random info about the differences
http://hhogear.com/index.php?page=what-do-i-need-to-know-about-my-oxygen-sensor
Ok here is a little explanation from gadget
http://www.customtacos.com/forum/showthread.php?p=569960 (read from post #7 and down)
So yeah, might be all yota's 99 and newer with AFR's... dunno 100% tho...

89 4Runner
3" BL, M/T locks, 33"bfg mt, bilstein, Kayline, tubebumper, toyotafiberglass panels
TBI: Elocker,3.4 w/ORS,b+b,S2Sstg2cams,arias pistons,P+P intake,TRDs/c,URDpullies+7th,downey headers,MAPECU2,WEGO WB, SupraMAF,walboro255,stg4clutch, EPaOo2 sim