Never heard of the diff ratio stamped onto the housing itself, could be though I suppose. I can give you a few ways to find it. Easiest, but slowest, would be to go to Toyota's website, go to the owners section and there is a way to send them an email. If you include your vin and ask your gear ratio they should send back an email with that info, I did this with my 00 just to see if they would respond.
Second, in the door jam there is an axle code, for 4Runners it starts with an A, something like A03A, this designates the ring size, number of pinion, 4 vs 2, and the gear ratio. There are conversion charts on the web, so just google toyota axle conversion charts and use the info from your truck. Some of the charts seem to be correct for Tacomas but not for 4Runners, so I don't recomend this method.
Lastly, and best, is the jack up and spin tire method. Jack up the rear and mark both the driveshaft and rear tire with chalk or tape. Then rotate the tire one complete turn counting how many revolutions the drive shaft makes. If it makes just over 4 turns you have 4.10, just under 3.90 and so on. Chances are if you have a 4wd auto you have either 3.90 or 4.10, it is also possible but rare to have 4.30 and if a 2.7 you may have 4.56.

Just saw its a 97 Limited, if you have the locker you probably have the 4.30, but make sure you get the right diff, the locker version used the older 8" diff, while the non locked had the 8.4, both are really an 8" but they are slightly different.