Tim,

With your truck at ride height; measure the bolt to bolt length. This should be the length of the shock at its mid point. That is half way between its shortest and longest length. This is not the most important measurement though. Select a shock that will not bottom out before your truck bottoms on the axle bumper. With those two things in mind; you should be able to select something from their catalog. Also measure the bolt size, I think they are all the same, I could be wrong.

54 Chevy build pics.