John, for an aileron version that stunts like a Cap 20 or Sukoi the 074 would be great. Just be sure to put a funky lookin' sunburst scheme on it....
Encan, she sure looks good in the pictures. I'm sure you can iron out the glitches and wind up with a fine model.
What size wire rods did you use? If they are 1/32 then you won't save much over that by switching it out. If they are 1/16 then you can save a bundle off that nose weight by switching to something like pull-pull string cables. The only other thing I wonder about is what did you cover it with? If the material is very heavy then ripping it off and recovering with something like So-Lite or one of the other tissue like plastic coverings would help quite a bit. Remember that one oz in the tail requires that 3 oz in the nose. If those pushrods are 1/16 wire then you can probably save about 1 1/2 of that 3 oz of nose weight. Also are your servos as far forward as you can get them. On one model I did a few years back I had much the same problem as you. Since it had a deep fuselage I mounted the servos high in the cabin area and forward under the leading edge of the wing. The receiver and battery pack then slid under the servos from behind. If your servos are mounted to the rear and they are the larger "standard" sized ones then you can help yourself a lot by redoing that part by going for the smaller 1/2A sized servos such as HS81's and moving them forward as I've described.
Another thought to help cure the heavy pushrod blues assuming you did use the heavy 1/16 wire and that long lengths of bare wire are exposed. You can try to swap out the heavier rods for some 1/32 wire. Where the wire is exposed outside of the tubes you can stiffen it up by backing it up with short lengths of bamboo shishkabob skew material bound to the wire with a few ties of thread that are fixed by dribbling on a little thin CA. Just be sure you leave enough free wire showing that it can move through it's entire motion range without the stiffeners hitting the ends of the tubing.
For next time you want to use rod and tube the idea is to make the tubing as long as you can right up to having a little sub bulkhead at the immediate rear of the servos and as close to the control horns at the tail as you can manage. Exposed lengths of 1/32 wire that are up to 1 1/2 inches long should be fine. It's stiff enough that you won't get any buckling on a slower 1/2A ship such as the J3. The idea is that the wire bound inside the tubing is supported and will not kink or buckle thanks to the support from the tube.
In the end 21 oz is about 2 or 3 oz heavier than I would like to see but in fact even at 21 it's still going to fly fine but the power off thermalling will suffer a little. If that wasn't high on your priority list anyway then don't sweat it.
PS: After looking closer at one of the pics I can see that you already have nice small servos. They aren't as far forward as the COULD be but they aren't bad. About the middle of the wing chord it seems. But I also note that the pushrods DO look quite fat so perhaps there is something to be gained there.
Also I'm assuming that you can fit the battery pack up into the nose so it's quite far foward? If not then that will help a lot. And last of all if you can mount the lead in the front of the cowling just below the crankshaft housing that'll help minimize the amount you need as it'll have more leverage. Another thought would be dummy engine cylinders that are filled with the weight you need. That would be very close to being as far forward as you can go I would think.
If you want to have a go at moving the servos forward and switching to lighter pushrods I have a couple of ideas. One of which is to switch to .045 or .050 carbon fiber rod. Carbon is very stiff and weighs next to nothing in these sizes. Just rough up the ends and epoxy on the hardware you need. I also have an idea for extending the support tubes to put them closer to the servos but that'll take a sketch to show you. If you want to try it then I'll take the time to do the sketch.