Welcome to the site. If your stock frame is in good shape Ridetech makes a coil-over and air bag system for that truck. If you wanted a new frame and modern suspension Morrison should be able to help you out. There's several companies like DJM and others on Ebay that also do lowering kits, I'm just not familiar with them or how well they work.
https://ridetech.com/product-categor...100-and-f-150/
https://artmorrison.com/products/custom/