Converting the 500s to multiple unit operation would have been a interesting task because as built their controllers were mechanical drum type only, they were linked mechanically across the cab for the LH and RH positions.
MU would have needed significant additions to the control circuits, certainly not impossible but a bit of added complexity.
Did the gear come from redundant locos or even H type trams?
I was a Mechanical Fitter, so I didn't know much about how the electrics were done. I recall they were fitted with a 830/600 style MU stand, a purpose made MU cable, and the usual MU air brake piping, to the A end only of each loco (they always worked nose to nose). Plus a hose for the throttle air to the speed piston on the governor. I recall some of the 500's being retrofitted with an electronic load regulator, but this was early to mid 90's so I think the MU mods to these loco's predated this. I do recall the pair being shopped frequently because of problems with them not loading up together.
Just getting back to my previous post, I spoke with one of my colleagues who used to shunt with the pair. For the sake of historical accuracy, while I remember them as "Bib and Bub" (from a workshop perspective), the Traffic and Loco boys called the pair "Bill and Ben". They shunted Dry Creek North yard, and often worked the "Runner" to Islington Freight Centre and return. I recall them in full cry (for a 4 cylinder EE!) departing the Creek with a hefty load past the MPC. I always took an interest in 527, as I was involved with it's overhaul at Islington in 1985 (the engine was ex 502). I think 527 still exists and resides in WA, so I presume the connections would still be evident.