Quote:
Originally Posted by nbpro
1987 chevy 4x4 12 bolt rear end with 3.73 gears with 31 spine axles
swap in to a 1981 gmc with a 305 engine. 10 bolt 2.56 gears th350c transmissions

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Are you sure it has 31 spline axles? I thought the 12 bolt had 30 spline and the pre-new body style 10 bolt had 28 spline.
The 12 bolt has an 8.875" diameter ring gear and the 10 bolt is 8.5". I don't think the gears will swap between the two.
You can easily find a 5-lug rear end that will fit your truck with better gears or just get the gear set & carrier from a wrecking yard and put it in your existing rear end.
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69 C10 shortbed stepside 400 small block - built like what a super sport truck could have been
https://67-72chevytrucks.com/vboard/...d.php?t=484426
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