Bitter taste of defeat! So much coolant in the oil pan.

I feel like it's in the timing cover area. I have seen eaten up timing cover, where it bolt to the block,(block coolant passages) causing coolant to run straight into the oil pan from the timing cover.

I have done the same as you and forgot a bolt on the timing over/water pump, that installing the bolt didn't stop the leak.

you need to look real close at ALL gaskets there and then put that part back together. leave the thermostat hosing off, and see if you can fill the block up to that point without it coming out the oil pan. if you can then that problem is fixed.

Install the t-state housing and fill it up the rest of the way. If it leaks, you know the problem is above the t-stat housing.

If it won't fill up to the t-stat, whatever level it stop at, is the level of the block to investigate.