I believe the manifold is the same between the 18 to 25 engines, if you look at it with the carb off you'll notice there isn't much room to enlarge it.

I attempted to run the engines I have ready to go on sunday, but then my starter battery died (only got it to fire once hand flipping, my arm is still sore from trying too hard) and the weather turned, it's been too cold and dark when I have had time to try agian this week, I have friday off to go to a RC swap meet (where I'm taking the engines) so I'll probably run them friday afternoon.

I think these things turn out pretty clean when converted, I'll get pics up of my conversions here in the next couple days, I took some just need to get them off of the camera.