Your 12 bolt looks stock. My
79 Big 10 rear looks exactly like your 12 bolt rear. It is a 3:07 rear.
You will not find identifiers on the pan. Look on the axle tube b/w the hog head and passenger side rear wheel--in the front. They say that is where they are supposed to be but i never found one there.
To answer your question as to rear ratios, my dealer manual for 79 pickups show the following.
for c10's without California
If your vehicle is rated for 4900 to 5300 GVWR (see door plate)
5.7 4 bl 2.56, 2.76, 3.07
for 5400 gvwr
2.76, 3.07
High altitude trucks usually had 3.73
Now if yours is a big 10 like mine:
3.07 is standard it is rated at 6050 gvwr You could get a 3.40 or 3.73
3.73 were on the big 10's rated at 6200 gvwr
305 cid 2 brl usually favored the little higher rear, like 2.76 and 3.07's.
The stock horsepower ratings were depressing. At 85 degrees the 350 had 165 hp stock at 3800 rpm with 270 torque at 2000 rpm
The 5.0 305 2brl had 140 hp/ 240 torque (This wasn't offered in california)
SgtDel
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