1998 Vauxhall Corsa not starting

Turn the key to the run position,not cranking,now can you hear the fuel pump driving then switching off in a few seconds?
If answer is no,down the rear right of the head is the ECU and wiring harness,on top of the ECU is a brown wire terminal connected to the alloy housing with a torx screw,this is the main earth for all ecu functions and the injector realy and the fuel pump relay are triggered by the ecu grounding at this point.
so run a temporary wire from this earth point up to the battery earth and retry.
I've seen a coulpe of jobs similar to yours,same engine,cheap test.
Shrinking rings heh?that's a new one on me.

I would start by retracing what you have done, most importantly valve timing,and all wiring and sensors, check for spark and fuel suspply.
As for the shrunk rings and 1000 pounds, LOL

check you have spark at the plugs first,then check fuel pump is running and injectors are switching (get a noid light for this ) ,if they are ok then check you have compression (disable the spark first unplug the coilpack you dont want stray sparks around when fuel could be coming out the plug holes).did you sqaush the oil out of the tappets before you put the head back on?post back when you know which one you are missing