Every time I think of making a gear hobbing machine the difficulties in making the hobs, not the machine, talks me out of it. The form on the hob looks more like an acme thread as I recall, but the difficult is cutting the relief. Picture cutting a very coarse thread with compound feed disconnected and moving in and out on a cam several times per rev to create relief behind the teeth.
Did you arrive at those dia's using gear formula? I think you've done it correctly, as both have the same dp, but the dia you get is the circular pitch, not the outside dia. Maybe that’s why it’s not laying out well.
There were some excellent articles a few years ago in making hobs in Model Engineers Workshop magazine. There was also a series on making a hobbing machine from castings, of bench top dimensions. Well worth tracking down some copies – most of the theory and practical aspects are covered