I am looking to restore a 1985 10 meter turbo hull.I wanted to take the blown inboards out and hang two outboards on brackets off the back. My issue is that I will be throwing the balance off by shifting so much weight off the transom.
My question is, can I move the fuel tank forward about 3 ft to offset the engine move? Has anyone had the floor up to know how big of a problem that would be ? I plan on moving the batteries forward also

I believe the fuel tanks are up close to the bulk head right at the helm. My 12 meter they are anyway.

So no way to shift a large amount of weight forward ?

Did any fountains of that size from the 80’s come from the factory with outboards ?

Yes they made a few 10 Meters with outboards.

That’s what I’m looking to put outboards on , a 10 meter,I wonder what they did different on the inboard and the outboard to valence it out

Balance it out.
I have a 10 meter boat with no inboards in it anymore
i wanted to put outboards on it

I did the same thing with a 25 Sonic and it would porpoise at mid range speed .I had to put big k kaefers on it

Looking at the picture it appears the helm and everything else is moved forward and the front deck is shorter . The I/o version has two vents on the front deck

2x O/B is lighter than a pair of Big Blocks with stern drives hanging on the back.

Depending on the bracket you go with, some are designed to add flotation to the stern albeit limited ( as with the Armstrong Bracket in the pic).

If you are looking for the "magic bullet" to set your COG - good luck as every components weight will vary just as each conversion project will have different components that will move the weights and balance all over the map when compared to a similar build.

You will have to get your engines hanging and then add or shift your weight accordingly as you close in on the completion..... the O/B fountains had more knees on the transom I believe