Hi Ed,
We all "talk" on the internet about what we would like to do, I know. I have great intentions and get about 1/2 of them done.

I know the ARF WM Intruder is longer, bigger, heavier, the wing is higher, etc than the old '70 Nats model, but it's available, legal and mine now. I just asked the question because I wanted to have the best available set-up for a good chance at reasonable success flying the model past Novice. I have to actually get it flying, too. I have to be able to do it in 5 to 7 days total. Hence; the ARF.
I have plenty of both types of engines, I'm just short on time and contests. We don't have any here in the West, so a turn-key, easy model is what I need for a remote location contest model. (At my parents house. They're old, don't tolerate me for too long. See a pattern here?) Most contests in the SE are SPA and the said ARF is legal, so it's a muffled .61 or an OS or Magnum, etc, .91 4 stroke.

I'll make some other model my "Classic Pattern Scale Ship". I saw just such a model at the AMA Convention in Ontario, CA last January. It was a Bridi Kaos with a Clarence Lee K&B .61 with one of those cool, old flow-through mufflers, a Rev-Up prop, Veco spinner, Kraft wheels, a Sig canopy, Williams Bros pilot and it was in clear dope and silk with colored trim and autographed under the clear by Joe Bridi and Clarence Lee. That was cool, but I didn't have a camera unfortunately.

Hope you get yours flying and post some info about the comparison between the engines. Sounds like a great idea.

Chris...