I can only speak for Arctics not Pacs but..
I had some concern over CofG when doing my build, the things I was adding and taking away would've moved the weight toward the stern and I didn't know if my bow was going to end up to flighty.
I even put a small access hatch going forward inside my forward under-deck locker. The idea was that I could get access to the tip of the bow to fill it with lead at a later date if required.
Turns out my fears were completely unfounded, the Arctic runs very flat in all conditions. I find most ribs are happy in a following sea but working hard to keep the bow down in a head sea. I on the other hand am quite happy in a head sea and feel more vulnerable in a following sea, the tendency for the bow to stuff is quite strong! Although I suspect this might have a lot to do with the design of spray rail on the bows rather than just weight distribution.
Obviously none of the above may necessarily apply to your Pac but I suspect needing more weight in the bow isn't going to be an issue.
In short, I'd say put the tank back where the old one was.