That is a really good price! (if the bearings and gears are in good shape).
Have you measured the spring perches? Cutting those off and rewelding will take more $$.
I plan on a truck 12 bolt in the future too.
Just plug in your tire height, rear gear and play with the engine RPM to see how the MPH reacts. (trans ratio will be 1 in 3rd gear, 1:1)
https://spicerparts.com/calculators/transmission-ratio-rpm-calculator
