47-55.1 47-54 1/2 ton leaf spring kit in a 3/4 ton

[dsraven]

if the supplier doesn't know, and you are just trying to hang some softer springs, you could simply use SOME springs from the 3/4 ton pack and not ALL springs.
there will be a spring pack bolt that goes through the pack and holds it all together. remove that bolt, thin the pack some to what you think you will need, then install a new bolt to make a tight pack again.
or you could get a new 1/2 ton pack and make/move the hangers. i suggest to mark the frame at the axle centerline before you start so you get it back where it needs to go
will you be using the stock torque tube rear axle in your build? if not, then you will need to change the rear spring to axle mounting to a more modern open driveline style, where the axle is tied to the springs solidly.
a factory assembly manual will have drawings of the different models of trucks and will show dimensions that could be compared between models. you also may find some dimensions in this link that has manuals from models of different years of chevy cars and trucks

https://chevy.oldcarmanualproject.co...esto/56134.htm