Been thinking about the time out thing. Is there anyway you could create him a safe space with pillows/cushions/beanbags where he could go to scream and hit if he needs to.
If he is still small enough put a gate across the door and you stay on the other side. you could call it a chill out zone, calming place, safe space, what ever you wanted. If he can climb stair gates perhaps a stable type door would work.
You need to be able to put him somewhere when his behaviour is out of control and he might calm quicker.
The only thing I will say is that he will probably throw everything around so if you need to use his room I would clear out any dangerous missiles.
I agree with Polter about recording strategies that work and also about trying to use positive language. For me saying use kind hands or be gentle didnt work that why I suggested Do not hit mummy, but it might work for your Ds.
Also with the marble/pasta in the jar, you shouldnt remove pieces because they have already been earned and removing them for later bad behaviour can lead to resentment and then the whole thing breaks down. If he thinks you will remove them, what is the point in earning them. I am not criticising, some people do say remove them for bad behaviour but it undermines the whole system. Remove other things if necessary. Again removing toys didnt work with Dd1 she would just play with something else. She was a nightmare.
Putting her in her room was the only thing that had an effect because she couldnt get any attention, positive or negative.
It is really hard work but try to talk about 3 nice things that have happened in the day before you put him to bed, it will make you feel more positive even if he doesnt engage.
Try to work out what sets him off and then you can start to work on reducing the effects. Dd3 for instance will meltdown if plans change so we dont tell her about plans until they are definite and often not until the day we are doing something.