I believe I saw a set for the 8 3/4 for sale on here. You can use the 7 1/4 but you have to oblong the holes to accept the 3" u bolt.
Here is a set, good guy to deal with too.
http://www.forabodiesonly.com/mopar/showthread.php?t=194564&highlight=3/4+shock+plates
You can buy the u bolts if you don't have them.
