Thanks Harvey. After a couple of hours the charger read 13.3, dropping to 12.8 when I unplugged it from the mains. The battery charge icon still only showed three of a possible five black bars though...!? Plopped the battery back in the car and the old girl came to life pretty swiftly given enough choke. Took her out into the misty drizzly gloomy evening for a brief spin, once it had warmed up the rough running soon settled. Fifteen minute jaunt out to one of the nearby lakes, parked her up for a quarter of an hour, on my return from feeding the ducks it sprang straight to life. Relief. Who'd've thunk it, eh? Just that little difference between 12.7 and 12.8 volts! I think the car was just sulking after spending a night out in the rain.
Of late I've had the filler spout on the upgraded radiator replaced with a new item, this time actually round rather than all squished and deformed like the state it was delivered in back in spring.
New 1 bar pressure cap, fits nice and snugly on the flanges of the new spout, and holds pressure. Properly.
No sooner had I satisfied myself that I had reinstalled the radiator and Kenlowe fan correctly and without leaks, and topped up with pink coolant, and "Wham!". The top heater hose split, disgorging hot coolant on the screen and street. Trailered to the workshop, heater bypassed whilst I waited for a pair of new heater hoses to arrive, nice and pliable new hoses installed, windscreen de-mister actually functions again! My handy-bit-of-unidentified-hose-found-lying-around short-term bodge hadn't faired well in just one week of use. It was just about to split at the hose clamp from the back of the intake manifold when I put the replacement hoses in. I don't think it would've held pressure another mile! Wasn't coolant hose, and couldn't take the heat for long! Lucky.
Next jobs include fitting an expansion tank and an MSD Street Fire ignition box, to hopefully cure the intermittent cutting out at idle followed by refusal to restart problem I suffer from time to inconvenient time! Steering idler looks like it needs replacing again too. Door weatherstrips could do with replacing. Doesn't end, eh!?