From single to twins.

[Cadeco]

I decided to change my single motor and install twins (will get 2 two stroke one due to weight), just get the following info,
"The American Boat and Yacht Council has guidelines for the distance at which twin outboard engines are to be separated based on the size of the engines. Their recommended centerline spacing between outboards in a dual engine installation is: V4 and V6 = 26-inches (660 mm)". Since I'm a bit dumb, i will ask. those 26 inches are from the center of the holes or from the interior support hole?

 

[Halfhitch]

That measurement is center-line of one engine to centerline of the other engine. For laying out the pattern on your transom you can measure from any hole on the transom bracket of one engine to the same corresponding hole on the other engine and you should get the same thing. Get a large piece of rigid construction paper or some such and make a pattern. Once you are satisfied that the spacing is correct and the hole pattern for each engine is correct, you can tape it onto the transom at the correct height and transfer the marks onto the transom. Don't drill the holes freehand. Be sure to use a guide to make sure your bit is perpendicular to the surface of the transom.

Something to take note of. I am not familiar with your boat model, but before you get to deep into this, make sure the splashwell is wide enough on your boat to accept twins. Remember that the hydraulic steering rams horns extend out wider than the transom clamp.

 

[seasick]

That is a fairly big job and I wonder if it is worth the effort and there will be a lot of effort and expense.. First of all, you need to make sure that your hull was available with twins originally.
The rigging manual will give you the drilling specs for the mounting holes and position, as well as the spacing ( probably 26 inches) . Verify what shaft length is required for the twins.
That's the easy part. Now you have to swap out the control box, add control cables, redo battery switches, add gauges and harnesses, probably replace hydraulic steering, install a second fuel tank pickup, and so on. You need two oil tanks, wiring and plumbing also.
One larger motor would make more sense to me and would weigh a lot less than two 2 strokes.