I have always wondered if you can have too much manifold heat. While my carb is off, I took a picture of how I use two lines to heat manifold. Is this overkill. I look into the manifold and it looks bright. I can always remove one of the lines

I don't think that you can have too much heat when using a plate and tubes for water or exhaust gas. The stock configuration has the intake and exhaust manifolds literally bolted together.

The problem with a cold intake plenum is that fuel can fall out of suspension and pool on the floor of the manifold. Once it has pooled there it is no longer being metered by carb/injectors and can make it's way into the cylinders on its own (enriching the mixture) or continue to collect there (leaning the mixture).

Tuning mixture implies being in control of the mixture.

I currently have 3/8 hard lines for hot water under my intake. Supply out of the head, suction I added a port in the water pump. Works great.

I tried using exhaust gas through the 3/8 lines like you are doing but it did not provide much heat at all. Sharing my experience. Vaporizing fuel absorbs a lot of heat.