K frame confusion

Back in time I wanted large bolt pattern on my 70 duster which started as a 4 wheel drum no power. I had access to a 73 3 speed 318 duster, swapped out k frame & rear end. So now power front disc no power steering. Now at my senior age I want the power steering back. Confusion starts when everything I read my manual steering box should be 1 1/4 output shaft, it's not 1 1/8. The steering shaft 3/4. My research tells me 1 1/8 was last used in 72. Also back in the day I went from sandwich motor mounts to cartrage type which started in 73 with 318's, started earlier for 340. I am relying on memory on donor car being a 73, I thought I was sure because of tail lights matched 73 I already had. So confused!!!!!!!