Hey RJ. On the CG, not really. On a bird like this, if the nose drops when holding at the wingtips, it is good to go. I know, guys use the fancy balance machines, etc., that is good for anyone. I just get it where the plans call for the CG, and try to get it level. Now I am into some bigger gas stuff, and really pay attention to what the other gas guys tell me. Depending on what you are going to do with the Intruder, sport flying, just play with the CG a little.
Some guys will keep moving it back a little at a time, for nice rolls. I am not a pro here, just average flyer.

On the engine, easy upright mount, saves a lot of problems. I use all OS 61SF's in these birds and other classic planes. Glass and foam stuff, mounted sideways, that is usually the way what I build was molded like that, most always beam mounts. Putting a 4C in there, maybe side mount may be better for you. Do you belong to the senior pattern association? Get on board if not, and even if you don't do any contests, you can get a lot of info from the newsletter, and talking to the other guys that fly this kind of stuff all the time.
The Intruder in the hands of a capable flyer, wins contests. You can use the battery pack to adjust your CG, fore or aft. On one of these, I have the battery pack up inside the canopy. On the rear mounted servos, I just did that for something different, and pull pull rudder. The later model Intruder ARF's have the tubes inside, and that works good too.
Vince