Call Manton first 951-245-6565 and ask them about a set for your motor. I've used both and I prefer Manton for almost every application including all out race motors
There 40 miles north of you and they have better products and probably better pricing than smith Bros. does now
I may have a complete set of that length in either 5/16 or 3/8 ball and 5/16 cups if you want me to look for you I will
Do you want 8.25 over all length or from the bottom of the cup to the tip of the ball (effective length)