8 3/4 replacement axle 5 x 4 needed

Looking for stock replacement axles for 66 Cuda with 8 3/4 rear. Somebody use to make better than stock replacements but all I can find are 5 x 4 1/2. Do not want to change everything over as I have 3 sets of rims for rear for different tires. Slicks, drag radials and street tires.Any ideas