Unfortunately its going to be difficult to determine what JIS (Japanese Industrial Standard) the splines were originally designed to. If memory serves me correctly the first JIS systems were a hodge-podge of non-Japanese design/machining methodologies. It would be hard, therefore, to find any specific, and reliable, information concerning these parts.
There is more to correctly designing splines than just knowing the OD, tooth count, and module. There are pressure angles/flat roots, circular pitch...etc. I'm no expert when it comes to gears/involute splines... there's ALOT to it.
You could probably make something work with the basic information but...
Ordering the Stubs from Ross (Modern Motorsports) would be more cost effective than trying to produce a one-off part that will likely cost you thousands of dollars to develop. Ross' parts are of the highest quality and will achieve the result you require at a fraction of the cost. Just my humble opinion (everyone has one).