I am trying to mentally picture how a motor with mild overlap is going to suck in water if it is mixing past the exhaust risers. It seems to me that the coolant water would have to fight the uphill bend in the riser and than fight the back pressure. After all that, it would seem to me that any small amount of water that got past would boil off very quickly in the manifold. Can anyone explain this to me?

If the engine has reversion, it doesn't necessarily suck in the water. So lets say that the engine mildly reverts at less than 800rpm. So each time the exhaust reverts it pulls a drop of water back up the exhaust 1/4". Now the engine idles like this for a while when you are coming into the harbor. Now that water has slowly walked it's way up the manifold. You shut the engine off and it runs down the riser and enters the engine.

I have a mild bog on acceleration out of the hole and I am trying to rule out reversion, doesn't seem like it is possible while the engine is running. It started to happen after I changed the springs for more timing advance in my DUI distrib. Anyone experience the same problem changing the intial advance from 12 to 16 on a SBC?

It all depends on your combo......but if you want to see something neat, while your engine is on the ground & running, point the timing light into the exhaust hose, and you can actually see "where" the water is in the exhaust, and the change when you give it a bit of gas.

(or maybe I was just seein things with the strobe effect)