69 340 k-frame and power steering questions

Going from manual steering to power steering requires a different (shorter) center shaft in the column, plus a different coupler. Depending on the years involved, you might need a different hose fitting on the P/S control valve. As long as we're talking '72 and earlier A,B, and E body P/S gear boxes, they will interchange not counting control valve fittings. Those can usually be swapped.