The swap you are speaking of will net you about 5 mph more speed. On the other hand, a Power Glide rear end will give you 10 mph more speed.
Other things to consider: the car axle will be a 5 bolt axle and your truck now has 6 lugs.
I did this swap with a Power Glide rear end in 1983 on my 37 and it does make a differnce (I now have a T-5 and open drive line). Now, however, the easier choice for you, in my opinion, is a set of 3:55 to 1 gears for your rear end. Then, there are no other issues to contend with.
Joe
