How far back from the LE is the balance point on your model? I built one from the MK kit back in the late '80s powered with an OS .40VF and it was a rocket. Mine was very light (all monokote). There is not much room in the fuselage for equipment; so it is difficult to move anything (like the battery) around. The YS .45 is heavier than the OS 40 VF so I'm a little surprised that you think it is tail heavy. Specifically, what does it do that makes you think the CG is wrong?
Please post a photo of your Arrow, if you can - thanks