Maybe you can just replace them. I don't know if this will work for you, but...

I bought a Goodmark firewall panel, and it had some goofy clips on it. On the original panel, I drilled the spotwelds from the back that held the original clips. On the Goodmark panel, I removed the goofy Goodmark ones and drilled a hole where the originals should go. Then, with a helper to hold them tight to the new firewall, I plug-welded the original clips on from the backside.

So, if you have access to a doner car or firewall, or can find one, get the original clips from it (cut them out?) and use those.

See... http://www.creative-machining.com/claylahatte//auto/1971cudaconv_java/#IMG_1891.jpg

Also, the previous few pictures.