Id make it as per your second drawing , but double the OUTER span !

What size are you looking at ? Tailplanes about right, better too much than too little.
speaking of twos , look at the ' Two Bits , push / pull twin boom for the ball park .

My P-38 , two OS 35S , is 78 span , 21 in between booms ,but its 8 1/2 : 1 A.R.

Other profile twins are 14 in engines , 48 wing , plus tips .

Youre going full fuse ? not profile ?
Gotta watch the THRUSTLINES on profiles are same distance from fuse , not nacelles .

Gotta nice colour shot of your G-1 Full Size .
Huges Twin was similar layout , two spans drawn .   

Robert, it's an interesting design you've chosen. Design elements in a semi-scale are almost always compromises. I would not move the engines, or, in the case of electrics, motors, so far apart. Several reasons come to mind, but the main one would be to try to keep the individual thrust lines closer to center so the asymmetrical thrust in an engine out situation  is minimised.

I also would try to keep the props closer to a scale location, by not making the nacelles so long. You only need enough legnth to fit a proper sized tank for the engine. Less if you go electric, and mount the battery as far forward as you can in the center fuselage.

The ideal tail moment usually falls in the range of about 1.4 times the wing chord, including the flap chord in that measurement. For example, with a wing with a chord of 10" and a flap chord of 2.5" at the MAC, a good distance, flap hingline to elevator hingeline, of 17.5" might prove to be right. A little adjustment either way can be considered, as it's really a "rule of thumb."

Trying to realistically estimate the final flying weight, will give you an idea of the wing area needed for competitive performance. 12 to 14sq. inches per ounce of weight is a decent wing loading to strive towards.

Once the wing area, and percentage of flap area is decided on, you can figure the size of your stab and elevator. 25% of the wing area, is another good number to consider, but as before, it's all compromises.

Last thing you should really consider is the TLAR (That looks about right) method of design. It's usually correct.

Id make it as per your second drawing , but double the OUTER span

But the page ain't big enough for that Mat!

Perhaps the span could continue on the back of the sheet?

E Gad. Depends if its a semi scale ' sport ' model , of full blown F2B .

Have you had a look at Mr Hunts Twin in the Electrical section .

My P-38 is a overweight somewhat irregular design. But its still
fine on the outer with the motors 10 1/2 from the fuselage Centre Line.
And if ones daring , its possible to do loops etc on the outer.
Maybe its the weight / inirtia holds it out there.

Inirtia is definately pressent, so requires forethought.Poss to get a lot lighter.

( see Bob Hunts 25 Oz. Airframe ! )

Other than that , the lines of yours are similar in plan ,
Just someones chopped the outer halves of the wings off . !

Have a good glare at Huges recosanance Twin ( Young howard huges)
 The things similar to yours ( as is a P-61 )
One versions got l o n g e r wings though .

Theres pictures of a profile one on this forum back a year or two .

The good thing about twins is you can re write the rules . . . .

It could be worse: you could have a hankering to build one of these: http://en.wikipedia.org/wiki/Blohm_%26_Voss_BV_141.

There are plenty of successful twin boomers around. Pick one or two and use them for the numbers. Alter your design around winners! As Hunt once said to me when designing a P-40 "Do you want a semi-scale stunt ship, or a semi-stunt scale ship?".

Think about that...

Good luck! and enjoy!

W.