Kevmor, you will need to notch your cross member. How much depends on what height you set your engine mounts relative to the frame. Either way, it is much easier to do by taking the cross member out.
Before removing, measure the clearance from a straight edge laying across the top of the frame rails to the top center of the cross member.
Then, take it out so you have room to install your tranny and use a jack to support the tail shaft and get it all lined up and looking pretty.
Now measure from the same straight edge across the top of the frame down to the location of the tailshaft mounting pad. The difference between this measurement and the first measurement is the amount you need to notch the cross member.
When I did a T400, I ended up notching about half way through the cross member. I cut a straight line 1/4 inch below where I wanted the tranny mount to be and then up at an angle to meet with the top of the cross member. Then I used 1/4" steel plate to weld into the areas where I removed the section of the cross member. I let the horizontal plate that the tranny mount would sit on hang off the back of the cross member and drilled two holes in it so that the bolts would go through it from the bottom and screw into the tranny mount (you will locate the holes for the tranny mount after you have slipped it back into position after welding the plate in place).
Wish I had pictures of what I have done, would be easier to show than to tell.
