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**pjmoreland** · 06-12-2023, 01:02 AM

I may be wrong about this, but I believe the wider rear ends had GM54 cast into the center housing, whereas the narrower design was GM51. That's how it was on a wide 1970 housing I sold recently vs. a 1968 housing I purchased to replace it. Measuring the width of the rear end would be the conclusive way to tell.

https://www.67-72chevytrucks.com/vbo...d.php?t=578793

Copied from the thread below:

axle width is 55.5 wide with 30.5 long axles on the narrow rear end. earlier rear end
axle width is 57 wide with 31 5/16 long axles on the wider rear end. later rear end

http://67-72chevytrucks.com/vboard/s...d.php?t=640514

06-12-2023, 01:02 AM	#5
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,355	Re: 12 bolt ring and pinion question I may be wrong about this, but I believe the wider rear ends had GM54 cast into the center housing, whereas the narrower design was GM51. That's how it was on a wide 1970 housing I sold recently vs. a 1968 housing I purchased to replace it. Measuring the width of the rear end would be the conclusive way to tell. https://www.67-72chevytrucks.com/vbo...d.php?t=578793 Copied from the thread below: axle width is 55.5 wide with 30.5 long axles on the narrow rear end. earlier rear end axle width is 57 wide with 31 5/16 long axles on the wider rear end. later rear end http://67-72chevytrucks.com/vboard/s...d.php?t=640514 Attached Images Last edited by pjmoreland; 06-12-2023 at 02:04 AM.