I’m also just an armchair aircraft and space enthusiast.
From what I understand, the Twin Mustang was designed as a long range bomber escort, to protect B-29 bombers on long range missions. The Twin Mustang had a range of 2,000 miles. One holds the record still for distance traveled un-refueled by piston powered aircraft. It took off, in 1947, from Hawaii and flew to New York in 14 hours, without refueling.
The Twin version was longer than the regular Mustang and had extra fuel tanks.
I should also add that 272 Twin Mustangs were made. It was also used as a bomber interceptor after World War 2 by SAC to repel Soviet bombers. It filled the gap for a few years until early jet fighters and interceptors came into use.