What ever happened on this? I'm late to the party, but am curious how it turned out.

I had a small water leak from the port exhaust manifold a few years back, near the rear two cylinders. I pulled the riser and exhaust manifold to find that the Permatex Indmar uses for the seal between the engine and the manifold had failed or wasn't probably applied - looks like they didn't use enough.
Coupled with that I think that my riser gasket was installed at an angle, allowing a small amount of water to leak out of the water jacket portion of the riser-to-manifold joint, and seep down to the manifold-to-engine joint.

So, I removed the permatex from the manifold and engine, and installed a paper gasket - works great. I also installed a new riser gasket. No issues since.

My only thought, in addition to what has already been said, was maybe your riser gaskets failed on both sides. It seems strange to lose both at the same time, but, anything is possible. Contrary to what Mike said, I know that you can get leaks from the water jacket in your exhaust down to the engine - luckily it wasn't a large amount of water in my case.