The 8.5" rears have little ears on the bottom, at the 5 and 7 o'clock position, that can be seen like small half-squares (triangles...wish I had a picture to show you).
They are VERY easy to tell if you know what to look for...you can even see them at night. Go to a car show or cruise night and look around. Most 1st gen camaros had the 8.2 (round covers, 10 bolts) and most GM rears from 71 and later had the 8.5".
The BOP rears had the cutout ears at the 3 and 9 o'clock positions...a bit stronger than the chevy version, I believe, because the axles are a bit stronger. But, make no mistake, they will grenade on you if you have much power with traction.
The 8.5's are pretty tough, like stated above.
As for your 70 F-bird...if it's an auto, it originally came with an 8.2 BOP (I think). You can get an 8.5 out of 71-81 F-bodies, or buy a new one for around $1800.
But, for piece of mind, you can get a 9" for a few bucks more, and be a lot stronger, or an S60...which is heavier, stronger, and probably overkill.
Lastly, I think the 9" has the best selection of gear ratios available.
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How many of you have driven over 340? 
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