They are readily available in the after market like you said .
They cost though .
129.99 at Currie
150.00 at Natl d-train
95.71 Chassis engineering
Even though car and truck 12 bolts are different , the splines on the pinion , and definitely the oil seal for a 1350 , should be the same , and jegs has 1350 yokes for 85 bucks NEW .