What size Driveshaft do you think I will need.It will be around 63" long.It is a back-half truck 14x32 tires motor has around 725hp trans is a Glide not sure on weight but I am guessing around 3200 lbs.

Mild steel, chromoly steel, aluminum, or carbon fiber?

That is a really long driveshaft and will require a fairly large diameter. I would contact some of the manufacturers to inquire. Mark Williams or PST are two of the top choices.