What is the best or easiest way to repair the broken ones?

Tom,

I was in the same predicament a while back. I mistakenly assumed that the 'studs' were separate pieces from the quarter extension. WRONG!! The 'studs' are actually cast with the quarter extension. So, if one or more are broken off, the only viable option you have is to drill & tap the extension to accept an actual threaded stud. You then use a nut with machine threads, rather than the 'speed-nut' type nut that comes as OEM.

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Bill Pritchard
69 SS396 Convertible
"Life is short; eat dessert first." - Ogden Nash
My low tech web page (http://home.att.net/~bpritchard/index.html)

I just performed this fix about 4 weeks ago. The way to go is to cut the old stud off then drill and tap to install a "new" stud. I've got a leg up on you probably, as I am a Tool & Die machinist with a Bridgeport mill at my disposal, however it could be done on a drill press. The trick is in the fixturing or "holding" of the taillight extension, with no straight edges it looks tough. the way I did it was to fixture off the bulb sockets using stand offs, or "spacers" the offset between the two bulb sockets was 3.0" I chose to do all the studs both sides so they would match, with 1/4-20. Be careful I broke through on one of the holes. E-mail me if you would like pictures.
Bob