Just got the new 12bolt together and hoping ready to rock, but unlike most of the rears I have, this one has no cups for the coil springs... only a flat plate with a hole in it. I have seen people use a zip tie to hold in the springs, but for a car built like mine and ment to race that is not acceptable. I have been told of some retainers for these type setups, but am unable to find anyone with them. Anyone have any pics of them or know where they can be boughten? Thanks

Sounds like you have a 65 or 66 rear with flat plates. GM still sells the tear drop shaped clamp fits inside the spring pig-tail. $7+ ea. Uses a HD thru bolt,washer and nut.
part number for one clamp only is 3763621
looks like this
http://1964-77chevelleparts.com/catalogImages/ACF22E.jpg

Thank you very much... just the info I needed. In terms of the axle... I'm not 100% sure what year chevelle it is out of... but seems to have the correct dimensions for a 68-72 so I'm not sure what the story is. Are their any codes on the housing itself I could check and if so anyone know of a place to decode it?

The year is part of the casting date. Look at the center section facing the cover. The code is next to the cover opening. Small "raised" lettering. A letter for month, numbers for day and last digit of year.
C256 is Mar 25th '66 for example. Looks like this
http://nastyz28.com/pictures/reardate.jpg

An early Chevelle is 54 1/4" inside between mounting plates or 60 1/8" outside drum to drum. 68-72 is about 1" wider.
The original ratio code is a very shallow code "stamped" into the (front-forward side) of the passenger axle tube.This is the 66 Chevelle format and list
http://www.chevelles.com/years/66/66rearcodes.htm

Code is G280 so it must be a 1970. Interesting. Wonder how it got flat plates instead of cups. Thanks for all the help.

Well hopefully the 64-66 springs are the same diameter as the 68 and up springs... or else we are gonna have issues. Thanks again.