Just about all of the aftermarket suppliers now have dropped axles and/or modified springs. Truck Shop & Brothers come to mind. Axles are about $400+ and the springs are about $300+. I'm not aware of any dropped spindles for these trucks.
Also, I seem to remember that you have to relocate the tie rod above the spring when you change to lowered springs or axle. This may change the steering geometry somewhat.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine