The reel locks are prolly gummed up, or rusty. Mine pull out ok, but if you don't get it out far enough the first try, you do have to reel them all the way back in, and start over.
The F-body conversion seems to be popular, and they work just fine.
Brian(redwingvette) also did it on his several years ago.(scroll down to almost the bottom of the page, and click on the seatbelt pic.)
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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"