416 issues - losing patience

I have more luck drilling 2 holes in the thermostat a scoop def. will help and then back to the block was it all cleaned inside ,before and after machining to not plug the cooling system any wheres , and I have also had same problem that turned out to be the head gaskets were plugging my water flow, just a thought ive had it happen to me ,new isn't always correct as some 1 stated cook that thermostat once ,had that problem before also GL hope you find the problem soon