You are asking about a wide bed, not a narrow bed, correct? The 1973 F-250 pick up is a different body style than the 1970 trucks. Body style changed with the 1973 model year trucks. The inside dimensions of the two beds are similar, but due to the differences in bed construction, they are not identical. The width between the wheel wells is a bit over 48" on both and the beds are both a bit longer than 96" with tailgate closed. Starting with the '73 model year Ford started "rounding" the corners where the inner bed sides join the bed floor.Ford also changed the frame width on some trucks, starting in '73, so there is a chance the '73 wouldn't directly bolr to the '79 frame. Hope this helps.