Update: oil can arrived late on Friday ...... filled with oil, did not take much perhaps 100ml, then ran with no sparks for 30 seconds - nothing registered on the gauge..
A couple of points Jeremy...
1. For what it is worth, all mechanics, amateur and professional, have favourite tools, whimsically chosen. I have both an oil can (pump type of course) and a clear syringe with markings. For this task, I prefer the latter as I see/measure the contents and the plunger allows me to pressure the contents to any degree I feel called for., I can also use it to suction liquids. I find it odd that you could not fill it more than 100ml. That seems no more than the capacity of oil relief valve passage. Luddite?
2. As you know, these engines (prior to the GEMS/Motronics variants), have low oil pressure in original format At idle, it can be as low as 12 and you did not get to idle. As well,especially after a lost prime, it can take time to show. Frankly, as much as we have hopes for this way of priming, if you have fears, move directly to the Vaseline.
3.
CODICIL: I work this morning with a memory of one of my first repairs (with my late 1984 Plus 8 EFI) more than 30 years ago.
All pre-GEMS and Motronic LR/Rover V8s stock originals have your/our oil original oil systems. Not the most solid system
(later changed to a crankshaft-driven oil pump with other sadder weaknesses). Ours start with a nylon covered aluminum sprocket that holds a notorious timing chain. These components stretch and stress the camshaft, prejudice the timing and cause premature camshaft wear. (actually the original 1984-1986 Vitesse EFI camshaft is surprisingly good, better than most popular aftermarket fast road camshafts) . As well, the system (all engines) causes the interface gear to fail with its teeth coming off behind the timing cover. No warning sign other than some odd noises from the timing cover for a short period,
that you cannot hear with the engine turning and the oil pump stops turning. It was very early on in my Morgan life.pre-GoMoG..but I touched upon it.
https://www.gomog.com/allmorgan/camwear.htm The various damage manifestations can be avoided by moving to a duplex chain. I have used them on all my Plus 8s for the last 400,000+ kms. I mention this only as I don't want you to get to a point where you are dismayed, not because you are proceeding wrongly. It requires the removal of the timing cover which can be done with the engine
in situ and if you are there anyway...
Lorne
P.S. I am still curious. At the time, Morgan offered two options for Plus 8s, EFI or carb. Which do you have?