Thank you Andy for the tip - but yesterday I bought the biggest black battery (cranking amps) that I could find at Kwikfit, which with the sticker off the front and the cover screwed down will look just fine, I think.
Anyway, back to the starting issues.
First problem I managed to solve was related to there being a spark through the king lead but not at the plugs. This turned out to be due to the rotor sitting too low and so circulating below the level of the cap contacts. The rotor was too long at the lower end when I got it and had to be ground down before it would engage with the slot on the top of the distributor shaft (Elizabeth at Omicron tells me that they have to do this - the modern caps are to some extent 'generic', e.g. made for several different cars). Clearly I had ground it down too much. A washer underneath the rotor raised it enough (with a little upward tweak to the rotor contact at the edge) to bring things into alignment, at which point I was getting a nice big spark at the plugs.
However, the thing still wouldn't start? Why?
The points had been tested with a light and the timing appeared spot-on...
But with the lhd valve cover (1-3-5) removed, turning the engine showed that when the flywheel was on the correct mark and the rotor arm was pointing at no1 ht contact, the engine was at the point where the exhaust valve had just closed and the inlet was about to open. Surely the timing was 180 degrees out?
I had suspected this before, but the distributor will only sit down in one position - though it looks as if the slots that it locates in are the same size, and the lugs on the bottom of the distributor shaft measure the same size.
So I connected up the plug leads 180 out and...
Bingo.
Great oil pressure.
Little observable propshaft vibration
I put the car (on stands) into top gear and ran it briefly at 50 kmh (no coolant in yet) - some gearbox noise, but bearable, and lots of sound deadening is not yet in place). The speedometer works!
Pushing the brakes slowed the engine.
So with some wheels on I could be driving it up and down.
Definitely a milestone. I have to check the Swedish paperwork but from memory, I think the car has been off the road since about 1966.
One of my daughters filmed the start-up.
https://www.youtube.com/watch?v=tMeJqt-knLI&feature=youtu.beCan anyone here suggest how I can 'correct' the timing so that the leads can be connected normally? What has been done wrong in the build??