The bottom line hear in my humble oppinion is will the company who makes the boat and it has to be assumed they know what they are doing ,
Will they warrant the boat when its done with your own ideas factured in,I suspect not.
You may be lucky and get it right and make improvements,which will mean the manufacturers will be thinking your a genious,My guess is out of the 10 people who move there engines around and try and make improvements to another persons boat design they end up with a odball,and they become the only collector of the boat, in the main.
You have to give rib designers and boat builderes credit for what they do,and they know there hulls and designs,and what works and doesnt.
You can get away with a diesel in the transome on some boats as they were designd with the beam and can take the weight,but to try and move a engine forward cos you think it will stop a sea from comming over the bow? is not recommended unless a person who knows your boat and design and weight tables can demonstrate it works better than a inboard at the stern which if you get it wrong will not be too bad,as most desingd ribs have the extra boyancie anyway.
Thats my take on this project so far,unless it transpires that Humber will warrant the project and the boat passes all MCA tests and RCD cat B then I am sticking to my oppinion.
Good luck anyway,Its not my boat and I have explained what I would do in the same situation.In the hope it stops somebody doing the same withought proffesional advice or the support of the designer/builder.