Well, Tathepilot, that operator has one very unique airplane there. I don't know what the second BE-18 they have is because there is only one Garrett-powered Beech 18 tail-wheel conversion in the world. It also happens to have an eight foot long fuselage stretch (four feet in front of the wing and four feet behind). The original registration was N231LJ. The last time I saw it was about ten years ago in Willow Run, Michigan. It had no engines on it and someone told me then that it had been recently ground-looped [a not unlikely possibility].
The airplane was the result of a rather nebulous deal between Gordon Hamilton (an aircraft modifier in Tuscon, AZ that did several Twin-Beech conversions) and that loveable softy and all around nice guy, Connie Kalitta (a freight operator). I do not recall what dash number Garretts it had on it but I do remember that they were rated at 715 shp. I flew that machine several years ago, and it is capable of handling a lot of weight and bulk with ease...but not legally. Due to a dispute between Hamilton and Kalitta before Hamilton had finished the approval process, the gross take-off weight of the airplane was only certified at 11,280 pounds. They had intended to have a G.T.O.W. of 12,499 pounds. This cuts into the payload a bit as you can imagine. With full fuel tanks and one pilot aboard, you will be just enough under gross to be able to take a Jepp case with you. To be fair, the airplane can hold a boatload of fuel [I don't remember how much].
The good news is that in spite of its appearance, the airplane flies nicely. The ground handling in this airplane is significantly more forgiving than the many PT-6 powered, unstretched conversions of tail-dragger Twin Beeches that Hamilton did. That being said, you will still find this airplane quite a challenge if you have no prior conventional-gear proficiency. If the company instructor is a very good one and you take your training quite seriously, a conventional gear checkout can be completed in this airplane, though. If you ever get the inkling that you have the ground-handling mastered in this airplane, you are about to receive a very rapid advance in your aeronautical education. The airplane can be operated quite safely as long you avoid a cocky attitude. I guess that's true of any airplane, but this machine excells in keeping you humble.
To avoid confusion, let me tell you about the many different turbine engine conversions of the Beech 18. There were two modification outfits that did turbine conversions: Volpar Aviation of Van Nuys, CA and Hamilton Aircraft Corporation of Tuscon, AZ.
Volpar did two versions. The Volpar Turbo 18 was a low cabin (C-45 or Beech D-18S) tricycle gear airplane with Garrett engines. In regards to performance, they are screamers. The Volpar Turboliner had Garrett TPE-331-101 engines, tricycle landing gear, an eight foot long fuselage stretch, the eight inch raised cabin of E and later model 18s, and the windshield of G and H model 18s. The 9 Turbo 18s were built for Air America and used in S.E. Asia. The Turboliner was designed as a 15 passenger commuter and freighter.
Hamilton Aircraft converted several tail-wheel 18s to Pratt & Whitney Canada PT-6-20 and PT-6-27 engines. The main fuselage was not stretched but a long needle nose was added that contained a 750 pound capacity baggage compartment. [The forward compartment was needed because the increased payload could not all be put in the cabin without taking the c.g. out of the aft limit]. This conversion was called a Westwind I (not to be confused with the later Israeli Aircraft Industries Westwind I and II jets). Hamilton's Westwind II was essentially a copy of Volpar's Turboliner with Garrett TPE-331-101s, the fuselage stretch, and the nose wheel. The one and only Westwind III is the airplane you described and it has the Garrett engines, the needle nose, the stretched cabin, and a tail wheel.