Cranking and running Norvel engines

I almost never start an engine anymore rotating the prop forward. A flooded engine will start and clear the flood as well if you back flip it. But, everyone has their own techniques and what works for one doesn't work for others. You certainly can flip forward if you choose as this is the way the spring starter is designed. I would try both methods until the engine is up and running. The engine is timed to run one way. It will only run backwards if it it flooded. It usually runs backwards for a few seconds, pops and instantly runs forward. Rusty, Henry Nelson made a few different plugs. The hot plug has a large element hole surrounding the element compared to the notched hex plug the HD plug. There's also the NLO2 plug which is essentially the HD plug. There is no difference between the two. There was yet another Nelson which was the earlier NLO2 but it had a different post which looked like a Glo Bee post with a ceramic epoxy around the post. These were older and you probably won't see these unless someone has old stock as they're not made anymore. I don't feel the plug is the issue here.

I recommend the HD plug as it has a better heat range for these engines and handles a variety of nitro percentages. You'll be surprised about how cool these engine run which is why you need to get heat into them initially providing short burst of rpm's. After you've painstakingly spent the past few days doing and taking in all the info that everyone suggested, the engine in my opinion should be up and running now.

The pinch in these engines are amazingly tight. This is the most problematic step which is getting over the hump and heat cycling the piston cylinder to alleviate this initial problem. I thought I even heard you say the pinch isn't readily as noticeable as it was prior. The engine should be locking to the point you can't turn it during this stage. This is why the heat gun can be your best friend. The all castor could be masking that at this stage and the additional head gaskets are doing the same. At this point, I feel the all castor fuel is certainly boosting your compression which is only enhancing the problem.
After the engine gets a bit of time on it and you want to run all castor, so be it. I don't feel it's necessary as some do and I'm not disputing what works for others. I'm merely suggesting to try the 20% 50/50 fuel and see. Ken