CCI makes the only shafts I'll use. They do steel and aluminum for myself. The guys are the smartest I've seen, in the decades I've had drive-shafts made. They've been involved in everything with powered shafts...including nascar and marine applications.
Tell them what you're doing...and they have it handled. They also machined up my hub for my NAG1 conversion [trunion], to a slip-spline shaft in my `cuda, as well. Very smart, very friendly, superlative work, and priced very fairly. It's a family business. Tell them what you have, pertinent specs, and what you're doing. They'll let you know what you need. Measuring chart/instructions on website
They're about a 1/2 hour away from Mancini's, who just sell parts.