According to Morgan's web site almost all their fuels have 17% oil but I've heard they mix by weight which makes it actually about 14% (feel free to correct me if I'm wrong). If you must use Morgan fuel then the only one I'd use would be the Jet 7% which they say has 20% oil (30/70 castor/synthetic) which if mixed by weight gives around 17% actual oil content. But seeing oil is the life blood of an engine I wouldn't use anything that didn't specify exactly what the oil content was.
http://www.morganfuel.com/omega.htm