Thanks to your many clues, Duggy...Ta-Daa!!!
It's a Ryan XV-5 Vertifan

Well done it is.

And the prize of course.

This weeks headache.

Have fun

First Clue - "could carry 4,500 kg (10,000 lb) of bombs to a round-trip mission of 16,000 km (10,000 mi). Requested performance was a maximum speed of 720 km/h (450 mph), cruise speed of 443 km/h (275 mph), and service ceiling of 14,000 m (45,000 ft)."
??

Next clue - After 11 September, the aircraft was grounded because of the difficulties involving the gear box and propeller control; the aircraft had by then completed three tests for three hours and four minutes of flight testing.?

Next clue "armament consisted of twenty 0.50 caliber machine guns "

Last clue - "used two sets of decelerons, elevons (for pitch and roll) and split flaps for landing"

The Northrop XB-35?

Well done Harry it is.

LINK -To a good article http://www.fiddlersgreen.net/models/aircraft/Northrop-XB35.html

I read an interesting pilots description of flying these wings, I think it was the YB-49, with the pilot saying back then that ATC had a hard time tracking them on radar!
And the prize of course

Have fun.