SP #1153 was in fact a TR6B "calf" built as #4653.

SP #1114 is not a TR6A cow, but a dynamic brake equipped SW8 built as #4609.

The railroads were having issues with the unions, who were claiming that each diesel in mu was a "locomotive" and as such required a separate engine crew. The railroads and the builders avoided this issue for a while by connecting hood units together with drawbars. It wasn't unusual to see an A-A, A-B, A-B-A, A-B-B, A-B-B-A set being considered "one" locomotive. After the union issue was settled, the drawbars were replaced by couplers allowing them to mix and match. In many cases, additional modifications had to be made, like adding batteries to B-units that had previously used jumpers from the adjacent unit.

The cow-calf switcher arrangement was a similiar issue, plus the railroads saved the cost of having a second cab and some assorted equipment. The TR6 was EMD's version of a cow-calf SW8.

I have run a TR4, which is the cow-calf version of the SW7. This set was never modified, and the calf was connected by a drawbar. The calf did not have a handbrake, or air brake equipment beyond a brake cylinder relay valve and air supplied bythe mother. There were no mu connections except between the cow and calf. Running them on the main at 45 mph with the calf leading was a blast!

SP bought the EMD TR6 demonstrator and three more sets. They ran on the NWP for a while as road units, not sure where else. At some point the calves where split from their mothers and assigned to dynamic brake equipped SW8's for the Roseville Hump.

My questions:

Why did the the original sets get split up? I assume there was an advantage to having dynamic brakes on the hump? Parts lists show this as a 540a DB system - probably wouldn't develop more tha 20,000 pounds at 10 mph. Did these get 65:12 motors and earin for hump service?

Were the SW8-TR6B hump sets connected by drawbars or couplers?

Were SP's TR6 sets built with full mu?

Portola has TR6A #1100 ex #4600 exEMD demo. Is it still missing the lower rear cab windows that TR A units did not have compared to a regular SW.

Nice photo - sorry for picking nits.