You will have fun with the repairs and calibration. There is a huge thread on the forum on these scopes. Including putting a heatsink on U800. Indeed you need airflow without a case! But i've also been told that the failing of U800 has to do with the manufacturing. The older ones are made by Tek and don't fail (that much).
The 2465 is indeed missing the shielding of the PS. There is no Dallas chip, but instead there is a very early EEPROM, called EAROM. As for serial numbers, Bxxxxxx is only Beaverton. They were made in other places; the 2465 in five according to the service manual (US, Guernsey, London, Sony/Tek Japan and Heerenveen in the Netherlands). My 2465 is from Guernsey. Every location has their own serial number counting i think.
I'm not so sure i would prefer the B model.... Dallas chips that go bad (but an easy fix), leaky SMD caps destroying the pcb's, PLS logic that can loose it's content (seen it in a 2710 SA, noticed at least one of those in the video) and failing U800 chips.