Vince, I would leave your arrows at the 29" length. An 1 1/2-2" beyond your rest is fine. You should finish up with an arrow wt. of approx. 355 gr. with a 100 gr. tip. If your original arrows did in fact weigh 463 gr. you will pick up some significant speed and yes I think it will be enough to match or exceed your current KE.
As far as cutting your arrows. If you can have a shop cut them. It's not that you can't use a dremel with an abrasive cut off wheel to cut them it's cutting them square. Unless you have a way to affix your dremel to a board or piece of angle and then rotate your arrow into it like the way true arrow cut off saws work I'm afraid you will not cut them square. I'm assuming you don't have a squaring tool such as one made by g5. You could make a squaring tool by using a fine file affixed in a bench vise and then checking it with a square. Squaring the end you cut is important so if you do decide to proceed go slow.
Do you have a fletching jig?
Dan