347 - I'm sorry, but I don't know a whole lot about chassis dynos. Which brand of dyno can give you such a torque figure? I thought that they could only give you a "Tractive effort" reading - somewhere around 5,500.....
Anyway, 620nm = 450+lb/ft torque. That sounds a little high for your engine combo. If you were running more compression and more camshaft, I could see 450. I'd guess that you'd be around 380lb/ft = 515nm. As is, it sounds like you have a nice combo that's making enough power to get you into trouble out on the roads.
Craig