Let me heap some more bad news on ya'

Sorry, but that model is a .46 size. And it comes from the mfg pushing the scales. I've got a bunch of .46size and have weighed them all. (If you are already squirming in your seat from reading this far, then don't read farther.)

The engine you've retrofitted will probably pull the airplane as well as the Evo did. You can usually estimate what size FS you can retrofit by taking half the displacement of your 2stroke and adding that back. You started with a 46. Half of that is 23. Add 23 to 46 and you got 69. A .70FS is about equivalent. So far so good.

But most 46size airplanes that fly good are usually under 6 pounds. A lot of people argue that wing loading matters. It does. But it's not the only thing that matters, nor is it the most important. Overall weight is really more important than wing loading. Yeah, yeah, it's splitting hairs, but it's those hairs that affect landing speed, climbing ability and some other stuff.

My heaviest 46size is under 6 pounds. It flies good. I've flown other guys 46s that were around 7 pounds. I was flying them because they didn't want to. OK, that's a rough way to put it, but basically true. They wanted me to figure out what was wrong with the airplanes basically.

Where am I going with this? I think I forgot.... grin......

You don't want to add weight to that airplane. No way. Don't. It's so dead simple to move a battery, that ought to be done without thought. If that's not enough, move the RX, but don't expect miracles if it's a new one and an ounce or less. Standard servos are usually a bit over 1.5 ounces each. A lot are close to 2 ounces. Move a couple.

If I were you, I'd look around for somebody to sell the P51 to. My Tiger2 is the heaviest 46 in the hangar and it's "only" 5lb12oz and flies great. But I can definately see it's weight working when flying it. I just finished a KYOSHO P40 and put retracts in it. It weighs 5lb7oz and flies good.