Yeah, ya prolly need to drop the inner fender to do it right. There's a bolt WAY down underneath the box, and on the outside, near the fender.
I had no tolerance, for messing with rusty inner fender bolts, so I ground off, or drilled out, the bolt, from the inside of the cab, and replaced it with a hex stud (like Moroso sells for valve covers), and a nut lock-tited (the RED kind /forums/images/graemlins/smile.gif ) on it.
That way I could stick it through, from the outside, put a nut on it, and tighten it all from the inside, by puttin an allen wrench in the stud, and turning the nut with an open end wrench. A one-sided fastener, if you will...
I prolly wouldn't do that, on a nice truck, but my Blazer is pretty beat
/forums/images/graemlins/wink.gif
BTW: MY blazer is a '72 and should be similar to your '71. Seems you're getting alot of answers from people with 2nd gens...
-Marty