Well, darn, I hate to be a wet blanket here but if I were looking for a rear end upgrade I think the '58 car would be way down on the list. They used a coil spring/control arm set-up that would require major modification to work in your truck. Not saying it can't be done but it would be a lot of work. There are other popular swaps for rear gears. One is to change the ring/pinion in your stock housing to a 3:55. Other options would include a mid/late 60's 1/2 ton rear which gives you the 6-bolt lug pattern that matches the front (I have a '69 with 3:08's in my '53) Camaro, Firebird, Nova's are practically a bolt in but change you to 5-lugs.
Do some searches here and you'll see lots of different approaches to the gearing issue.
