I used Bailey Morris for getting my propshaft made. I had the sliding yoke assembly, and the dimension they wanted was from the flange of the diff' to the back washer of the gearbox. I sent the yoke to them, they returned all, and everything fitted beautifully.
Unfortunately, i can't make any comment as to the strength of it, as i haven't finished the kit yet.... bummer.
http://www.beales.uk.com/Pages/cobra/cobra_home.htm