is it a case of move bits n pieces that are in the way,check the gap on spark plugs,unbolt old ones ,bolt in new ones ,?
is 0.7mm the right gap for a standard classic sti my00

 

Remove the air box and you have access to 1 side
Remove the water bottle (you can balance this on the battery) and you have access to the other side.
Crack um undone and yes 0.7 should be fine, thats what mine were and i think anything up to 0.8 is fine.
Double check everything is tightened and attached up properly b4 putting everything nack.

 

if you get the car jacked up its alot easier from the bottom, without dismantling anything, iirc you will need a 2" extention bar.