Been reading this massive thread here. Want to give my two cents worth of info. I've been in the '66 geek mode for 20+ years now and majority of the ones in my garage are '66s:
1. I truly believe the Budd bodies were manufactured through 1967. Even though many of us associated the eyebrow grill with the Budd body, I believe that not be the case. That little indent under the driver's seat introduced in 1968 is one clue. Notice there is no manufacturer tag one the bronco till Ford put their own on it in 1968 in that recessed little box? Before that there was nothing - no Ford, no Budd. Almost like that was neutral ground between both manufacturers not to label - Ford did not make the body but Budd is not making the bronco. Perhaps an agreement from the start.
And if Ford did start building the bodies sooner than 1968, you would have thought the recess would have been stamped by then for mid-year 1966. No reason to produce the like Budd and then do another version later in 1968.
Also, I've noticed that there are a lot of surviving 1966 and 1967 broncos around. And from what I remember, the bodies sure seemed to have faired much better than later dated rigs from rust. Not all of them, but a lot! Could this be due to 'thicker gauge'" metal or that good old fashion red oxide primer? Were the bodies dipped? I've noticed a lot of runs under the painted rigs of early years.
2. Forward facing rear shocks - I've only witnessed the first few months in 1965. I own early '66s and a later '66. The later has the rear facing rear shocks. And I've studied other four/five month build and later rigs, seeing all had rear facing shocks by then. With that, I'd like to see people post their rigs with forward facing rear shock and build date associated with it.
3. Hard doors on a U13 were definitely an option. I've seen hard doors with frames and window guts. I've seen a U13 hard door with no frame, no guts - just the latch to keep the door closed. If you want to make sure they are original doors, remove one hinge from the jamb. If paint behind the hinge, usually indicates that it was added or a repaint It should be just primer behind that hinge from the factory.
As for the hard top, not necessarily a documented option but could have been added. Special DSO will never be able to reveal but that was merely a sheet with "add ons" written and tied to that rig. Ford would do anything to fill an order. As for this top, not a correct one for that year so must have been added later.
4. The motor looks like it was swapped out. '66 blocks has "C5" engineering codes on them. And the 170s did not have writing on the valve cover. Count the number of freeze plugs too. The 170 had three, 200 had five. (Correction on freeze plugs from fordfan!!! Thanks buddy)
5. As for the eyebrow grill, not sure what when on there and why the "eyebrows" disappeared after three to four months production. But when Ford was rolling out the bronco for model year 1966, they made a ton of broncos in the first three months. Perhaps the die to stamp the grills simply wore out in that area and by the time they re-tooled, erased it as it was one less item to contend with?! Still a mystery!
I've been in the '66 geek mode for 20+ years now and majority of the ones in my garage are '66s. And back then, 1966 broncos had no respect in the bronco world. There was only a handful of us that would discuss and pursue these rigs. Many criticized them because of the less desirable drivetrain. The "hard to find" '66 parts of today were worthless back then. I knew different and glad I did! Easier for me to restore a '66! Tim