Dang.... I've been working on putting together a cruise control system for my '70 on & off for the last 5 yrs. The only part I don't have is a good 70 b-body cruise lever (have a rough one with the guts hanging out....still looking)
Anyway.... from what I've learned, there is a subtle difference in appearance of the knobs for 68/69/70. I believe it's in 70 that you have 2 wires coming out of the stem instead of 3 wires. I believe 70 is also the first year that doesn't have the vacuum hose going to the cruise control unit. You can tap into a standard brake switch for your cruise, but the stock cruise brake switches have an extra spade connector. Each cruise control bracket is car-specific.
Each body style has a different shape/length of arm, though I've seen a guy cut up a C-body cruise lever & a B-body standard lever & graft them together. Some levers will "fit" and work, but not be exactly correct.
I may have some extra parts if you need something. I have a whole plastic tote of cruise stuff I've collected from swapping & salvage yards over the years.