Hi
Well done for sticking with it and finding a solution!
Block feeding is best done without draining the breasts outside of LO's feeds unless you have to, to avoid mastitis or are trying to build a stash - the full breast is what helps reduce the milk supply to a more suitable level over time.
There are foods that increase your supply that you can cut out - oats is a big one.
I found my blocks got as big as 12hr - basically one breast for day, one for night
I also found that when DS was having intestinal symptoms - blood & mucous in stool, that it helped if I pumped, mixed the milk up to make sure it was all balanced wrt fat and water, etc. and bottle fed for a few days, then introduced feeds from the breast slowly - BT first as OALD was not as bad at the end of the day and middle of the night feed last as that's when it is worst. I was hand expressing about as much as you've expressed there too - it takes a while for your body to slow down the production but it will make a big difference from what you've written.