Need help and advice with a cavity in the water jacket inlet

Hi,

i own a 91 nissan maxima with the vg30e motor and im rebuilding the top end

im cleaning up the mating surfaces for the gasket that goes between the intake side of the heads and the intake manifold, the intake manifold flows coolent from it into the the head and thats when I found heavy build up and what apperd to be a small crack in the water jacket inlet which turned out to be cavataition, right where the mating surface is for the gasket

it somehow appers that it was filled in with an epoxy, I only relised it when I was cleaning the mating surface, and I saw what appered to be a small crack but when I investergated it, it was a chunk of epoxy as it seemed that had been put in their to fill up the gap, im think wether its posable just to keep using epoxy but its only rated to 100 or somthing degrees, or can someone fill the gap with a tig, I know that their is a high chance of the weld being pories, but would it distort or warp or crack the head
also I found out that it really is epoxy since I did a continuity test with a test light and a mutimeter to see the resistance, and it really in epoxy that chunk I took out

but it might however not be epoxy after all, it might be limestone
but cant tell if it limestome or scale build up or epoxy

im on a budget and replacing the head really isn't an option so whats your input on this subject

i have atached a photo of the port that is the problem for me, I have left the peice that I found in the cavity and its also in the photo resting on the intake port rim