[Tx Firefighter]

You've got 73-87 front suspension and brakes on an earlier frame. Very common and Rustbucket has the wisdom in his information.

Now, my question is, why have you mentioned multiple times buying new arms ? You have arms already. If you want to lower the truck, get drop spindles and/or drop springs. No sense in messing with new arms. Just program yourself that any front suspension or brake part you buy shall be for 73-87 fitment. And, again like Rustbucket covered, 73-87 had two different thickness brake rotors. Measure yours and buy spindles for whicher application you have. When you go to Summit or wherever and catalog your new drop spindles, just use the model year 83 or so and select your spindles. There will be a notation in the part description for "1 inch brakes" or "1.25 inch brakes". Choose the one you need.