Dozy is leading himself astray with conspiracy theories, just like Mahon. For example, he links the missing pages from the ring binder with the issue of whether the crew were certain of their position, when they are not actually related at all. Let's assume that one of the missing pages had the final waypoint at 164E, in the middle of the Sound. So what? We already know that Captain Collins thought that's where the waypoint was (unless it was a murder/suicide). The real point is that the universal rule for a 1970s DC-10 captain was that the inertial nav system was not sufficient for a descent below MSA (which is why the captain pretended to be visual). If he was actually certain of his position before he went down, then he had no right to be. And if he was so confident in the accuracy of the AINS, then why was he so pleased to receive the offer of the radar-assist?
The correct precedure was reasonably obvious, wasn't it?: Stay above MSA to the waypoint. If still no VHF contact, go to the Dry Valleys. The only issue would be whether the TACAN alone could be used to confirm the aircraft's position before going through the cloud layer. Given that it only provided distance information, it would be a 50/50 situation, which means you would think about for a few seconds and then forget it and head for the Dry Valleys.