fitting an upper to a lower?

[bcass]

I just bought my first FAL kit and receiver (entreprise arms type 3 receiver). I put the pivot pin in and tried to latch the upper to the lower and the lower will not latch at all. I tore down the lower and removed the butt stock and dove in to the frame locker. I removed all that to get a better look. It seems that the lip of the frame locker is too low to go over the nub on the upper. What's the best way to correct this? Should I order a new frame lock and see if mine is out of spec / bad? Or are there a few key places on the LOWER that I should file down to help the upper pivot in place a little lower. It looks like I have < 1/2 a cm from being completely against the lower as far as it can go. that might be enough to get the frame lock to engage the upper. Thoughts?