Transmission Output Shaft Question

Hi all,
I have a A999 lock up transmission I just picked up and I did a search to find out what i that would need to change and be aware about when changing from my original 904 in my 72 Scamp . There's not a whole lot different but i know i would need a 1968+ crank for the converter. I think i read something about the output splines for the driveshaft slip yoke are different. Are the 904 and 999 output shafts differently splined and if so where can i find the proper slip yoke?
Are the slip yokes the same length so i can reuse the driveshaft?
Thanks
Unless I'm misreading your post, why would you need to change the crank for the converter. All A999 and 904 converters have the same size crank pilot from 1968 on. The pilot (or snout as some call it) measures 1.810". Only the pre-68 cranks have the smaller, 1.550" pilot.