GPM Front Diff Joints
 

I just got done putting aluminum front diff joints from GPM in my gen1 vette. The long one was very difficult to get in. I had to lay it down on the cup end and press very, very hard of the differential to get it to snap into place. After that i could no longer get the little center pin in place, so I left it out (Murphy's Law of Spare Parts). The short side was easy and the 2 for the back were easy, but that front long piece was a royal pain.
A couple other members of another message board said GPM's seem to not be all the precise when it comes to 1/28th parts. One of them suggested Atomic Mods aluminum parts.

i will also recommend atomic mods parts. they specialize in 1/28 scale so you shouldnt have a problem with anything. they also have excellent reviews on all parts.

Ya true atomic mods does have good reveiws but they sell GPM parts too