I am building a Mongoose to put a MK6 on, adding 2 inches fuselage length, and will glue vertical webs to the spar. The mongoose will be small wing area though. It should be fun.

A Nemesis II would be fun also. Mr Rush is building Nemesis for a Nelson .36

Then there's foamies,, Gotcha Psycho. Or maybe a Russian prebuilt fast, not sure if they are still available.

http://pages.prodigy.net/gcleveland_grsmodels/_import/pages.prodigy.net/gcleveland_grsmodels/index2.html

Greg

Here's what I used to use (the Ivanhoe). The other is Ed Brzys' more straightforward approach. Both are similar to what Phil Cartier sells.  I recommend a big foamie in lieu of some of the "classic" designs that were intended for G21's.

Spruce spars and vertical grain shear webs

It depends alot as to what type of model you want to fly, as in a fast combat model on a bladder, or a so called "slow" model on suction. You will not find the MK6 vibrates very much if at all as long as you make sure to balance the prop, I believe all "slow" combat models at least what the club I belonged to used were all profile fuselage I believe the rules called for that or the way they were written made them the only real competitive models so vibration had to be absolutely minimum, so a Flite Streak maybe with a little beefing up of the front and of cause glued with epoxy should work well on suction, there is alot of fast combat model plans out there alot of them foamies which means buying or cutting out foam cores.
 I am sure there is going to be corrections about what I said being as I really didn't know the rules that well just flew what everyone else flew in my club. 

Yankee Nipper

http://www.tulsacl.com/YankeeNipper.html

Jim,
How about a Challenger? I have two sizes. 360sq and500 sq.  If you still build from balsa that is.
Let me know.

Gordy