Chain vs sprocket must go on in correct order to get chain on the sprocket. No tensioner mounted.
I forget that all the time.
Maybe chain first, then sprocket.
Both follow each other when cam is entering from the side.
Rotate engine without plugs so you can verify T at 1:4 with cam in correct position. Can be done before rockers are mounted. Do it again when all rockers are on their shafts moving the valves. A simple mistake will cost.