Those 244 chips are notorious for failing - with it just out of the board and the KB disconnected does that improve the situation? The keyboard pin header does have -12v as an output so maybe a short?
The VDU chip was available for about £18 from littlediode. They do not have a listing at the moment but, I am sure a contact will allow them to be found - they were SFF96364 not as per the ETI article - I have also seen them listed as CRT96364 - it needs to be an A for 50Hz
https://www.littlediode.com
My Pin 2 is a fairly rounded 1MHz clock - photo attached.
I am sure Ian once said that the display appears blank if IC70 is faulty.