About the only way to tell without a tag for sure is to pull the chunk out and count the gear teeth. That accomplishes a couple of other things besides determining the ratio - it also determines the axle spline count as well as which, if any Equa-loc or in a few cases, Detroit Locker plus the condition. The standard rear end if you didn't specify something else on your order sheet was a 3.50 (my local dealer and I had a fight about that problem on my '65 w/390 PI, I ordered an Equa-loc with 4.10s - they had to do a dealer install
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