I put the valves in before the tappets and blocks, it is a pain compressing the valves and getting the keepers in, harder if the tappets are in the way. The cam can be rotated to a no lift position for all 4 valves of each block. The blocks with tappets can be removed with the engine assembled, but a bit tricky to keep the followers from dropping out as you do it. I am already forgetting, but I think when assembling the blocks I angled the blocks in so the cam would keep them from falling out, then the tappet plungers could be depressed enough to roll the blocks into position. You might have to pull them in and out again if the allowed tappet clearance isn’t within spec – it is a very wide allowance though since they are hydraulic.