By Madman springs I'm guessing you mean Madman Autococker springs.
If so you are likely going to have to mess around with your spring combinations in order to get one that works since Autococker springs are longer than Nelson springs.
Sounds to me like maybe you're main/valve spring combo is where you should start.
With those internals I would say try a lighter valve, stronger main and see if that give you any results.
Are you having roll out troubles as well?
Have you looked at any of these threads Historic Nelson Tuning Threads