Ok, so you already know the original length of the drive shaft. Unless you're going with a huge lift, I think you'll be fine with the stock length of the splines, but that's beyond my knowledge and a question for a driveline shop.
To measure the static length you need, bolt both ends of the driveshaft to their respective flanges. With the 60 on level ground, measure from the center of the forwardmost u-joint cap to the center of the far one in the rear. Just like measuring the wheelbase of a car. That will be your new baseline length for your driveshaft that the shop will need. I would expect them to have a formula along the lines of the Pythagorean Theorem to calculate how much you need for the slip yoke. They may want to know how much droop and compression your suspension is going to have. That, of they'll just know from experience.
As far as how much of the spline section shows at rest, I only have one stock height 60. It's an '87 with a single u-joint, but I imagine that part is close enough to the same. I'll shimmy underneath and measure it when I go to my shop.
