One thing to add is the locking clips for that hold the cables on the cable bracket on the trans are the same. I was scrounging through a yard trying to find mine originally because the trans was already taken out of the altima that i got my shifter and cables from and they threw everything in the dirt. I only found one. I ordered 2 from greg and used those and they were both identical. Worked perfectly. Awesome writeup man.
As for your question about the C-clip SR20DET91, did you already bolt the case down to the bell housing? If so Its probably pushing against the clip not allowing it to go in. I think your supposed to lock that clip on the stack before bolting down the case fully to allow movement of the stacks to get it back in. If everything is shimmed up correctly then there is no reason it should be difficult. Coheed can probably chime in on it as he has done it twice now.
As for your question about the C-clip SR20DET91, did you already bolt the case down to the bell housing? If so Its probably pushing against the clip not allowing it to go in. I think your supposed to lock that clip on the stack before bolting down the case fully to allow movement of the stacks to get it back in. If everything is shimmed up correctly then there is no reason it should be difficult. Coheed can probably chime in on it as he has done it twice now.