944 aluminum-alloy with bumpstop 6,816 kg
944 aluminum-alloy without bumpstop 6,810 kg
(these are the 2 different styles of alumium-alloy trailing arms, not the same arms with the bumpstop removed!)
Both measured with the wheel-bearing (800g) and the stock 944 inner bushing in place.
I haven't measured my stock trailing arms yet, since I'm too lazy to disassemble the drum-brakes :P
The difference will mainly depend on the brakes you want to run.
Some more weights here (in Dutch):
http://www.keversite.nl/forum/viewtopic.php?f=5&t=17066