Looking at your build photos,
Check your sparkplugs to make sure none are fouled, oiled up, have a huge gap or a very tight gap.
Check the plug leads are not tracking down the plugs or to ground somewhere else.
Check the HT leads it looks like some have been replaced already. The red Repco ones are crap.
Check for air leaks between the air flow sensor and the throttle plate.
Check for vacuum leaks around the intake manifold.
What is your fuel filter like?
Try and get hold of a fuel pressure gauge and check the fuel pressure when it is playing up.
See what you find?
Also loving the white paint sillhouette on the grass around the car.