Thanks Jon. I considered using the ERR Offset generator as well, but the sound was pretty faint from mine with the volume cranked up fully, so I bit the bullet and put in the Alco PA sound set. Also, the prime mover would run at full RPM all the time, right?
Another member here is taking the stock couplers and hacking off the coupler portion and doing the same to the Trackmobile couplers and bonding them together. That might give you a slightly shorter coupler, maybe 1/8" shorter from what I measured.
I've been asked about doing upgrades, but I don't really want to be cobbling up those electrocouplers, it was fairly time consuming. I did learn a few things doing mine, and I think if I ever do another one, it'll be easier. Trying to use the stock centering springs was an exercise in futility, when I abandoned those, things moved right along. I realize now that the piano wire springs work better than the stock springs, and they're easier to do, so that's the way to go.
I have brass rod now, I'm going to take a whack at making railings for mine.
A somewhat related question, does ERR now list the ERR Offset Generator? That was a slick piece of work, just wondered if they'll offer it at some point. 
