Rocko1012 - Other than slight mods to get the rear 77 tank to fit correctly in the 70 Frame, Everything fits - No problem. I recommend using an earlier tank.
That is exactly what I am in the process or doing with my 69 Bronco. The engine, trans, transfer case, steering column and power brake booster are from a 77. All in great shape, just rebuilt. 69 Fuel tank remains. My 77 will have different drive train installed.
Once it is all said and done, the average person will have NO idea that my 69 Bronco did not come with an C4 automatic transmission or power steering. Although, members here will know.
Since the 69 will be rebuilt with all original Bronco parts, it will look original with no modifications to make it work..