Joe,
Its easier than that. Snatch the torque tube out of your 54 car rear end. USING YOUR ORIGINAL SPIDER GEARS, put the 55 car drop out member in the 54 car housing. Set your pinion angle with a bottle jack and the weight of the truck on the springs, stitch weld your pillow blocks in place and you are done.
There are plenty of mobile and welding fabrication guys that can come over and stitch it up for you. This should be a minium charge. However for a little more than the price of a guy coming over to weld it up for you, you could buy a 135 amp mig/flux setup and do it yourself.
Did you measure the sping perch distance on the 55 car rearend? A 56 car bolted up under my 54 and 52 cars and all I did was drill another hole for the spring locator bolt to center things up. You can buy shims in 2* increments if necessary.
Chris
