The locomotive in the picture below is a Brookville DES-70B. I've been intrigued with it for years partly because it looks amazingly like a BEEP - close to the same size and shape, just two axles. 600 HP diesel/72 tons. I doubt the BEEPtoy body is based on it, however, since the toy body has been around since the fifties (Kusan among others) - which I think is much longer than Brookville has been making this.
But I cannot find out how long these have been made . . . Brookville made a forerunner model of this they called the BL6 which was even slightly more BEEP-like in appearance, and perhaps earlier models before that one. I have been unable to find out - even wrote the company but got no reply - at least not yet.