The manual rack has a smaller diameter input shaft compared to the power. I cannot remember if it is shorter or longer. I think it may be the same. The adapters with the splines that go on the bottom of the rag joint have matching splines and will fit only the rack they are made for. I believe you could just change that piece on your power rag joint. Flaming river sells that part, I think, as someone mentioned.
I installed a used Mustang manual rack, that I got with tie rod ends and the intermediate shaft. It bolted in perfectly, tie rod ends and all. It did take me a couple years to find it, and if I was going to do it again, I would prefer all new Flaming river stuff.