Proto2000 do very "cost effective" Alco S-series switches, via Walthers. They can also be found new on eBay for under US$50.
Alco S-series switchers are slightly shorter than most end cab US switchers, but the ubiquitous EMD "SW" series locos,
(SW7, SW9, SW1000, SW1200, or the more modern/brawny-looking SW1500 and MP15 derivatives),
are other options which are available fron Athearn, Atlas, Proto2000, and other "plastic diesel" manufacturers.
If you are looking at doing "short 4 axle" locos, you could do a lot worse than the current centre-motor versionsof the Bachmann 44, 70, and newest siderod-driven 45 tonner mechs. However, in comparison to Dallas's conversion, the wheels on these mechs may be a touch small for those who put a premium on "engineeringly plausible" diesel-hydraulic or diesel-electric Gn15 mechs and wheel dia. (That's not to say that you can't easily replace the wheels on a 44tonner with something larger from the OO Bachmann Branchline range




All of these can be expcted to do 18" easily, most will look at 15",
and with some tweaking the shorter ones will run on 12" radii.
(I know, it's not the 9" and 6" that Gn15's are used to, but they are also over twice the length and axle-count of most Gn15 locos shown here on-list...

For the $$$, you recieve an oily-smooth low-speed crawler mech that should make even the most hardcore "mech tech" happy...
