I fully agree with Stu, searider is not a particularly sensitive for shifting in weight/balance, Having had the opportunity to do many trips with 4 kids/youth on board, have shifted/played with weights pretty much. In easy conditions, by having weight in the stern, the fuel consumption is little less that way, at least based on the flow meter reading on my boat.
But handling wise considering general usage, makes sense to have the tank more forward. My comments/worry for bow heavy in following seas might be influenced by my limited driving skills ..
If /when will do a console modification I would also consider a tank in the console. I wonder, how big tank was attached on Narcosis boat?
There is an E-Tec on the picture, is not that roughly 50 kg heavier than the Yam, so if one want to achieve identical balance to that one, think console needs to be litle closer to the stern?