If anyone wants to put a t-5 behind a 'y-block in a '54 (did '55 and '56 have X frames?), beware that it is a helluva job. That being said, I'm almost done!
I run a T 3550. Even bigger and heavier than a T5. I had to cut out the center crossmember, weld on flanges, so it could bolt back in. I use a whole pile of 5/16 grade five bolts with washers. I have had this set up for years, and it doesnt move around at all. No problems whatever.
Deal, I will post pictures of my swap. That crossmember gets in the way really fast. Taking out the fordomatic was a job unto itself.