Ok, had a skinfull last night because I was pss'd off with this, but looking at it with a (semi!) fresh head this morning, I'm going down to the project car to look at it logically as to why it won't start.

I've written down a list that may help me:
Symptoms
_________
Won't start after rebuild
Backfires like a beast - through the inlet

Possibly no spark (but hard to believe based on the above)
What we know
____________
12 volts at DIS pack
Fault code 19 exists, (even though it's never been fired up)
There is definately fuel at the injector rail
The engine earth is good.
What I'm checking today
____________________
1) Order of HT leads
2) Cam sprokets are in the correct keyways, and valve timing is correct
3) Try spare crank sensor
4) Check body earth
5) Try the spare ECU?
7) Double check there is a spark using a timing gun and seeing if it flashes

Check all sensors are plugged in and all connectors are in the right place and fully home.
If this doesn't work?
________________
Tow to remote location, pour petrol inside, throw match and leg it!
No - seriously, if anyone's got any logical additions to the above that may help in getting this sorted, I'd be really grateful to hear them.
Cheers!
James