Not starting - Firing on wrong stroke?

Just replaced the stem seals and went to fire up the car after being built back up and seems to be firing when the inlet valve is open? (won't start, backfires and seen fireballs out throttle body)

I stripped down the front end and redid the timing belt, had my old man who is also an engineer to check I wasn't doing something stupid and both agreed it was right (also turned engine over both ways and set back to original position and all marks lined up again)

Tried to fire up before putting all back together but issue is still there.

Only other thing I can think of is if I mixed up injector or coilpack wiring which seems unlikely as they are all different lengths so matches up to the cylinder? Is there anyway to test the plug by turning the cas to check the firing order?

Also are both inlet cams 100% identical. I'm certain I pit the same cams in the heads they came out of but is there a chance I messed up there?