Torque spec for steering box

[chevyhed53]

I have a rebuilt Saginaw-style gearbox on my '56 Chevy truck, which has a mid-70s front end. The shop manual for mid-70s Chevy trucks says that the nut on the pitman arm shaft should be torqued to 145 ft-lbs. But the info I got when I ordered a Summit rebuild kit for the box says 100 ft-lbs. The box is leaking at the pitman arm shaft, which is why I bought the rebuild kit. Is it possible that torqueing it down too much caused the leak by crushing the seals? And what is the proper torque spec?
Thanks!