400 SB Bellhousing

I have a 400 SB with an external balanced flywheel. When I try to install the transmission, (4 Speed) it will not slide in without hitting the fingers. Do I need a different bell housing, or an adapter plate.
The external balanced flywheel is thicker than a normal 350 flywheel.
How do I resolve this issue.
Ty948

I don't know what you're using, but when I installed a 400 in a 62 1/2 ton I used the bellhousing that was behind the original 283 and had no problems.