driveline question

I have been having problems with my driveline,

at the beginning of the year I had my th350 rebuilt, had no problems getting it in the car,
Now I go and replace my flexplate, When I took the driveshaft out, I had to pry it out with a big screwdriver wasn't too happy about that.

Now when I try to put it in,after I changed the flexplate, it does not set all the way into the trans so I can get the U-joints in the yoke of the diff., I have asked a few people and they said check the yoke and make sure there is nothing blocking it, OK done nothing there, I also took off the tailshaft cover, and cleaned the splines, still wont go in far enough, to get the driveshaft in.

any ideas about what I can do, or what might be the problem?????
thanks for your help guys!!!!!

**************
I was looking at it, and my question is,

Do the yoke on the trans have a type of soft plug at the back/bottom of them, if so, do they come in different sizes?????