Can an Aristo SD 45 find it’s way around a 180° 8 ft curve, without stumbling? Asking for a friend. 
I don’t really care about looks, as the curve is in in a minimally visible area, hidden by a “mountain.”
It can, but it could pull the following car off the track depending on length and coupler placement (ie long cars with tango mounted couplers).
Body mount, 830 coupler, 40 ft car. The 830 box has cutouts to improve truck swing.
Body mount to body mount, you should be fine.
SD45 with body mount Kadee coupled to 40’ car on 8 foot diameter curve:
(from Ted’s vignette on Kadee mounting on GP40 and SD45 https://elmassian.com/index.php?option=com_content&view=article&id=361&Itemid=405 )
Interesting coupler change on the loco. I did it that way on my first SD 45, some 15 years ago, when I first laid my hands on Great Northern 410. I used a medium offset coupler, rather than do all the back and fill that Ted recommends.
Ten years later, when GN 420 came out, as I started to remove the Aristo swingarm, I thought (yes, it hurt), I wonder if I could just place a medium offset coupler in place of the Aristo coupler. Sonofagun, it works, and it matches the Kadee height gauge, too. Well, close enough that you wont notice it from a galloping horse. Haven’t had any problems with it for years.
I had replaced those shaved plastic Kadee boxes on the SD45 with direct fit custom made CNC strong metal boxes that accept Kadee centerset couplers, springs & lid.
I had the boxes made for me by Datum Precision in Grass Valley, CA.
For detail info. see vignette: “Custom Made Coupler Boxes & Kadee Centerset Couplers for Selected Aristo-Craft Locos”
-Ted
Those look awesome, Ted, thanks.