Well, do I start with the good news or the bad news? Good news first, I guess.
Following a telephone conversation with Nigel yesterday evening I resolved to swallow my fears and get stuck into lining the distributor up correctly. I loosened off the 13mm bolt holding the forked clamp in place, and lifted and wiggled the distributor body and rotor arm until I had it where I wanted (rotor arm making initial contact with the HT lead for cylinder #4). After numerous clicks, the starter motor eventually caught and within a couple of revolutions the engine started and was off and running. Woo and hoo...!
But that was as good as it got, unfortunately. The engine sounded rougher by the second, there was a distinct exhaust blow noise (and this was after I'd had custom copper gaskets fabricated) and when I peered underneath the engine there was a steady drip drip of oil falling off the diff housing.
I honestly feel like I'm getting to the end of my tether. It's just one roadblock after another. I'll regroup and try and do some more investigation tomorrow, but right now I've really just about had enough. It's not helped by the van having a suspected faulty head gasket (or warped/cracked head) and we've got an 800 mile drive back on Friday. Plus it's getting harder to select 5th/reverse gears on the van as well.