I have done what you are attempting on a '49 and a '53 3100. What I did was cut the bellhousing crossmember off with a 6" cutoff wheel in two places, removing the center section allowing for clearance for removal of the automatic transmission from below.
I then welded plate steel flanges to the stub ends of the brackets (still riveted to the frame) so that I could reattach the center section of the crossmember 2 inches lower.
I then welded plate steel flanges to each end of the center section so that I could bolt it to the plate steel flanges on the stub ends of the bracket on the frame.
I drilled two holes through the plate steel flanges to accept 1/2" bolts. This will allow you to easily remove the center section to service the transmission or remove it.
