This is a Sabreliner 50 - the one and only ever built, in fact. It used the fuselage of a Model 40 and the wing of a T-39. But's a Model 50:
There are many planes uglier then this one. Super Guppy being only one.
I stand corrected and yes you are right. It IS a 50 model being a retired military airplane. With all of its mods, it could not be designated a commercial airplane like the normal 40, 60, 70 and 65 aircraft. So it was then designated 50 model. It is a unique airplane and I was corrected when talking to the flight department. You were right and I was wrong.
There is an even uglier and much newer plane that beats anyone in the ugliness dept: Boeing X-32 JSF. For those of you that don't remember this one just click on this link http://en.wikipedia.org/wiki/Joint_Strike_Fighter_program It looks like a venerable Navy F7U Cutlass delta wing fighter on a really heavy diet of steroids and zillion gallons of beer per week. No wonder they sent it to pasture.
If you take off the front end, this is a fine looking plane. I saw it in person not a month ago, it is in beautiful shape. Not the ugliest by far, most commie planes are uglier!