Here is my two cents as to how to kit bash a single into a twin. Been there done this and it works.
There are very few multi engine arf's and few kits, compared to the single engine types. If you want to get multi experience before the bank is broken on that multi engined warbird consider "bashing an ARF" to a twin. Yes, the twinstar and others are good, but small compared to the larger warbirds.
One way is to find a long fuse single such as .60 size ugly stick, put nose cone over the center engine mount and add naceles to the wings. Warning, the wing loading sky rockets!!Forties will not fly this well. Go to two .60's, add 8" to the wing and add wing plates on the end. The result flys well and was the subject used for the experimenting on twins.
Another way is to create a "100'stand off scale" F-82 twin mustang. Yes, World models makes a F-82 arf, but is still smaller than 80" .
One plane that works well is to take two Long John 40's, combine the wing to 82", two fuses side by side, I set my engine spacing at 12.5" to use 12x4 props, and a single horzontal stabilizer. Must make a brace to hold the fuse's inline for transport. I learned the knife edge circle with that one and still fly it today with two .45's.
Still another is to use two Ugly stick .60's and build as the Long John. Take the arf's wing halves and glue as normal, then shorten the center joint four rib spaces for only one new joint.This yields around 86" wing span. Two .60 two stroks fly it well two .90's are awesome! (More power.ARGG ARGG!!) Sheet the center and glass for additional strength. The horzontal stabilizer is formed useing the original stabilizers shortened in the middle. This type of two fuse system can either put receiver on one side and battery on the other, or can practice the concept of two receivers for redundant control. Again, must build brace for transportation to hold the fuse's in alignment and not break the horizontal stab.
The two fuse conversions should keep the props almost touching for better engine out characteristics..My twin Ugly stick is not close. The center line of the engines is 20" for more practice similar to a P-38 with wide engine spacing and I am using it for aerobatic flight, coupled engines to the rudders. Engine out is good due to the long fuse and larger rudder.
Whatever you do have fun with it, but practice before the first twin warbird on a cheaper alternative. Been there done that..don't do that!!!