Further update: After posting I checked 'AI' Claude in this case for Rover V8 tappet noise, it suggested that after running with no oil or standing idle for a period of time air in the 'lifters' could take a few minutes to be fully removed. So, just ran the engine again until hot and the tappet noise slowly disappeared! Phew! The oil pressure at tick over is just under 2 bar and around 3 bar at 2000 rpm. Not taken it for a run yet, that's tomorrows adventure!
Glad you understood my vaseline instructions. Your observed pressures are fine. The Rover Factory wants to see 27-35 psi at 2600 rpm with WARM oil. It can be much less at idle.
I use a Buick 215 device to adjust running oil pressure to what I preferThe tick is universal
assuming it goes away in a minute or so It is a characteristic of this engine and its lifters. If you think of it, 1-2 of the lifters will be always be fully compressed and drain down completely when you stop the engine and leave it for a while. If you don't use the car for a day or two, they will need to "plump" it/them up when you next run the engine. However, if the tick does not go away, there are other, sadder reasons for it. As a precaution, I would suggest you add a bottle of ZDDP after every (3000 mile) oil change. This
last of the flat tappet engines was made for this. The world changed, our engines did not in this area until the GEMS variant. (1998 in the US and 2000 in the UK)
Losing your prime is one of the most common experiences with this engine. You have been lucky. Don't knock it. You will have greater insurance against its recurrence if you use the GoMoG's Plus 8 method of oil changes.https://www.gomog.com/allmorgan/plus8oil.htm#Change I have not lost my prime on any of my Plus 8s with an oil change since I began using it 30 years ago. But I am lucky as well.
Hope you have a pleasant drive.
L.
P.S. Thank you for the pictures. I have saved them.
. Reminds me of an episode in the 70's painstakingly stripping and checking every hydraulic tappet on a Chrysler 383. Despite re-assembling with oil the noise on starting was deafening. Discussed issue with a friend who simply (and a little unconvincingly) suggested leaving it to run a little over idle if oil pressure showing which it was. After what seemed like forever but probably only a minute or so I noticed noise slowly then quickly subsiding. The ticking noise from one of the tappets, being the reason for stripping all in the first place, had dissapeared as well 
. Drove down the pub to celebrate. On return journey ticking noise re-appeared 
ho hum...