steering coupler replacement (how to)

I just got my U joint from Bryke. Smooth 3/4 side fits great. Spline side is way to big. Apparently what I have is a Chrysler 5/8 not 3/4. They have nothing that will work so I have to mail it back for a refund.

I tried Flaming River but they want $200 for the damn 3/4-5/8-36 spline U joint. - NO thanks.

Called Weller Racing and they have nothing that fits but are calling their manufacturer to see if they have something that'll work. Talk about a buzz kill.