turbo 400 clearance problems

Trying to put a turbo 400 from a '74 Chevy truck into my '70 Chevelle, I've got less than 1/4" clearance between the slip yoke and the floor board. Wondering how much clearance is normal and if the tranny is drastically different from a car turbo 400 dimension wise.

Make sure there aren't any spacers between the trany mount and the mounting pad on the tranny case. If I remember right the chevelles used a different tranny crossmember for the 400s.