I ran a big Hughes SFT cam in my 340 for over twenty years and in two different blocks. I broke it in originally with just the outer springs from Hughes. Put the inners in but they weren't enough pressure. Engine would float the valves at 7500. I don't remember exactly what I put in for a valve spring but IIRC they were about 220 on the seat and a little over 440 over the nose. Never had a problem with that cam running it to 8000. Sounded like a roller at idle too. So there is that. I still have that cam somewhere and wouldn't be afraid to run it again.