[blykins]

Are you using a bushing or a bearing?

If you're using a bearing, I've found that it's generally tighter to get in.

If your bellhousing has been lined up and you're sure that the measurements clear, then put a bolt in and see if you can pull it in with just a little bit of pressure. I normally wouldn't advise that, but I've had to resort to that before with a pilot bearing.