Actually the 4-6-6-4 has always had a single motor drive. The one I got just over 10 years ago looked like the one in the first photo, except it had the Boxpok drivers and skewed DC-71. It was the T1 4-4-4-4 that got to have dual motors.
Here's a Kato motor that would do great in your Challenger: http://www.ebay.com/itm/Kato-Ho-31-500-HM-5-MOTOR-1pc-KAT31500-NEW-/322286467595?hash=item4b09c53a0b:g:RPMAAOSwE0JY-318It's as powerful as a DC-71, and it's small enough to be an easy fit.
Or if you want something even more high-end, here's a Faulhaber coreless: http://www.ebay.com/itm/Faulhaber-2230-Coreless-coasts-like-has-ball-bearings-/151363268980?hash=item233df43174I used one of these in an old Akane 4-8-8-2, and it works great!
_________________________________________________________________
There's another major difference between the old one and the newer one, the newer one is dual motor, the old one is single motor - is it really modified?
I think you will have a hard time finding a can motor of equivalent power that is small enough in diameter to keep the driveline straight. There are small enough ones, for sure, but they won't have the torque of the old motor. Looks like quite a project to rig up some sort of spur gears to offset the motor shaft higher - but then you could use quite a large diameter can motor. Wouldn't do much positive for the noise though
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Top Image is the rear drive of newer 'DC71' style Bowser 4-6-6-4
Bottom Image is rear drive of older style Bowser 4-6-6-4
(I have previously posted that the Bowser 4-6-6-4 and 4-8-8-4 I resently assembled are noisey. At the advice given by several forum members, I have just let the 4-8-8-4 run. Going for 50 hours.)
Someone modified the older 4-6-6-4 and replaced the older 'super60' motor. I like the straight drive line but the motor hangs out the cab.
I would like to find a can motor that could fit without increasing the angle.
Has anybody used or have pictures of the old style drive line and a can motor?
Thomas