Castrol

Castrol is a good brand, I'm familiar with their 20W50, which I used pretty much exclusively until I got on the synthetic band wagon ten years ago or so. I always hesitate to make recommendations that would potentially put someone at financial risk or personal peril, of course, but if it were me, I'd try the Castrol 20W50 and see if you could see any difference. The 30W is what CC recommended "back when", but oil technology has come a long way since those owners manuals were printed.

On my 427s, I've been using Mobil-1 15W50 with good results. The 50 weight factor comes into play when the oil really heats up, and you should have a thicker viscosity at hot running temps with the heavier oil, which would most likely reduce blow-by and cook off too. What you are seeing and smelling may well be a cook-down by product (too). Since there are few applications for straight 30W these days, I wonder about the quality of the stuff.

Just a few addl thoughts.

regards, Paul