Both 69 and 70 Chassis Assembly manuals show both the power steering hoses sub-assembled to the main hose bracket with retainer, insulator and screw installed, the old easy of assembly scenario, and therefore do not document the screw. However, in the For Car Parts Illustrated Section 36.4 page 5, the screw is indicated as 40923-S, 5/16-18X1/2in hex thread cutter screw. As this screw is common to other power steering applications, 64-67, and shown with a -S8 clear zinc finish you can assume it is the same for 69-70. Occasionally Ford keep the same parts for multiple years. The -S8 finish "may" be -S2, phosphate and oil, as that finish is used as well on other 40923-S screws. I got the screw p/n, you can figure out what finish you want.
Jim