Hi following with interest - wierd?
You seem to have covered all the main areas;
Fuel in the pots - the plugs are still getting wet?

Spark at the plug - still there?

If so then immobiliser, cut-out are all ok.

If timing stays as you set it after rotating the engine several (many) times then the belt is a red herring (it will go out if its the wrong one). :doh:
The cam followers rely on an oil supply to work. When you checked them did you dimantle the two halves, clean check and refill them with fresh oil?
If one is sticking part open it can hold a valve off-seat?
Have you re-checked the compession since doing the followers.

As was said before - if the spark is on the right pot, the fuel is getting in and the valves are closing ok - it will go bang and fire up (start maybe?).
Pic's from Rave showing cam pin alignment and sproket positions for info.
Keep the updates coming.
Just a silly thought - you did not get the cams swapped over? (said it was silly)