Hurrah! At last, we have life!
Huge thanks to Mr Olds & Chris, ("Forgotten"), for spending the day at the lock-up today. Still got the electrical problems to sort out, but finally ...
finally, 2 years after the replacement engine went in, it burst into life this afternoon. Took most of the day to figure out why it didn't want to start & I'm not the sort of chap to point out that I suggested this morning that maybe the distributor was 180 degrees out, but...the dizzy was 180 degrees out.

Now statically timed to 6 degrees before Top Dead Centre, as recommended by Mr Phunkie for the Pertronix electronic ignition we've got fitted. The HT leads are now back in the proper positions, new cap & rotor arm fitted.
Problems-
a water leak from the inlet manifold, where the water temp' gauge screws in. I've screwed in a new brass adaptor & it looks like there's a hair line crack in the casting now that leaks under pressure. We poured a bottle of K Seal in the rad though, as recommended by Mr Kapri & others & just as we turned the motor off, it stopped leaking, so either the seal did the trick, (it takes a few minutes to work through the system & find any leaks), or the pressure immediately dropped enough for it to stop dribbling. 2 of the core plugs were leaking last time I filled the rad. Too much water everywhere to tell at the moment, but I'll dry everything off tomorrow & see if they've sealed too.
Very low oil pressure. Only 8 - 10 showing on the gauge, (I'm assuming that's psi), but nearly 30 when it's revved. I bought the engine from someone who'd rebuilt it to go in a kitcar, so I've no idea what's inside it, but it's the same oil pump as I ran before. It's a 1990s Discovery motor, but I fitted the front engine casing from my old 1970s SD1 engine cos the water hose layout was different. So it has the same oil & water pumps as before.
We had plenty of oil showing on the dipstick when we started, but it may be low now as it's circulated & filled the hydraulic lifters, pump etc. We didn't check it before we left, so I'll have a look tomorrow. That might explain the low pressure.
We fired it up several times, but the last time it was just a little hesitant to start, but we'd fitted the air filter by then, so it might be running slightly lean now.
Otherwise, all seems good.
I've just had the brake discs skimmed, so need to refit those before we can think of driving it, as well as working out why several switches on the dash aren't working, (no ignition light, no wipers etc). So I'll spend the next couple of days cleaning up & repainting various parts in the engine bay, then we'll have another go.
I'm a very happy Monkey though. Thanks guys.

Chris, delving into the engine bay, (small phone photos).