Motorman
I've found the Nelson and the GP Rossi's are similar in that to get the power necessary to run in the 14's they really need to rev. From experience I can say that you will want to run 29k on the ground mininum. If you have a strong engine, you should be able to turn around a 6.25" x 4.6" at that rpm. That will get you close. I would start with a 6.25" x 4.75" and go from there.
If your not getting at least 29k then you can drop the diameter down to 6" if need be and and the pitch down to 4.5" and not lose any airspeed (provided you have a clean model).
You don't really need a large disc area on an AMA Goodyear model. My best prop for my Gillott Rossi was a carbon Gillott Nitro Goodyear prop cut down to 5.75"x5". It gave a consistent 14:99 airspeed, with amazing acceleration off the start.
The thing to remember is that these engines hate to be lugged. They are timed to make peak HP at 30+K which is about what they should turn in the air, so try and run them at that.
Les