YOUNG GUN: Putting Nitrous on 318!!!

First, you really have to work to blow it with a 50hp shot and a mild 8:1 318. You can break it, but it's not that easy.
1. I'd say consult NX because you;re probably running too high a pressure to the plate, which can cause overrich, which is actually worse than lean with a mild system.
2. Timing was fine where it was. If the engine is in good mechanical shape 50hp is nothing to it. In fact 100hp is barely past something and it's pretty bulletproof.
3. cooler plugs are a good idea. It means they may show rich more than not, but you're not really looing for color. you;re looking for the burn mark, and for specks of aluminum on the porcelain. Flecks are a problem. Burn mark just helps tune.
4. Running on full kickdown pressure and manually shifting is not a solution. It's wearing the trans almost as fast as not running kickdonw at all. Get the right kickdown linkage, clearance the air cleaner, whatever you need to do but get that back working before you really fry the tranny. You'll do that long before the engine gets hurt at 50hp.