The fender tag will be on top of the left inner fender under the hood. You'd be looking at around a grand or so for an original Dana rear, depending on ratio. Reading the fender tag from left to right, bottom row, if the 7th character in (also the first single digit) is a '3', it's an original 4 speed car. The axle code will be in the 2nd row from the bottom of the tag, under 'AX', and should be '68' for a 3.54 Dana, or '98' for the 4.10. The 4 speeds are pretty rare; if it can be bought for anything less than 8K, it's a good deal. If there is no fender tag, the value would be considerably less. Another thing to look for is the condition of the chrome trim items- particularly the tailight bezels, trunk finish panel, and grille surrounds; if these need work or replacement, you're looking at a big financial hit.... probably bigger than the Dana. They are very hard to refinish correctly, and if you need to replace any of them, the prices are ridiculous.... when you can even FIND good ones! (and yes, I am talking from experience!)